If your audio is anything like my son's iPhone 6, the likelihood of a high quality result is low. You should get it to pass through Vegas with minimal  further distortion, however.

Complete name                            : C:\Users\John\Desktop\IMG_4585.MOV
Format                                   : MPEG-4
Format profile                           : QuickTime
Codec ID                                 : qt   0000.00 (qt  )
File size                                : 7.85 MiB
Duration                                 : 10 s 573 ms
Overall bit rate mode                    : Variable
Overall bit rate                         : 6 230 kb/s
Encoded date                             : UTC 2016-02-20 03:21:18
Tagged date                              : UTC 2016-02-20 03:21:28
Writing library                          : Apple QuickTime
com.apple.quicktime.location.ISO6709     : +38.7284-121.2382+052.187/
com.apple.quicktime.make                 : Apple
com.apple.quicktime.model                : iPhone 6
com.apple.quicktime.software             : 9.2.1
com.apple.quicktime.creationdate         : 2016-02-19T19:21:17-0800

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L4
Format settings, CABAC                   : Yes
Format settings, ReFrames                : 1 frame
Format settings, GOP                     : M=1, N=30
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 10 s 573 ms
Bit rate                                 : 6 135 kb/s
Width                                    : 1 920 pixels
Height                                   : 1 080 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Variable
Frame rate                               : 29.970 (29970/1000) FPS
Minimum frame rate                       : 28.571 FPS
Maximum frame rate                       : 30.000 FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.099
Stream size                              : 7.74 MiB (99%)
Title                                    : Core Media Video
Encoded date                             : UTC 2016-02-20 03:21:18
Tagged date                              : UTC 2016-02-20 03:21:28
Color range                              : Limited
Color primaries                          : BT.709
Transfer characteristics                 : BT.709
Matrix coefficients                      : BT.709

Audio
ID                                       : 2
Format                                   : AAC
Format/Info                              : Advanced Audio Codec
Format profile                           : LC
Codec ID                                 : 40
Duration                                 : 10 s 572 ms
Source duration                          : 10 s 635 ms
Bit rate mode                            : Variable
Bit rate                                 : 79.7 kb/s
Channel(s)                               : 1 channel
Channel positions                        : Front: C
Sampling rate                            : 44.1 kHz
Frame rate                               : 43.066 FPS (1024 spf)
Compression mode                         : Lossy
Stream size                              : 103 KiB (1%)
Source stream size                       : 104 KiB (1%)
Title                                    : Core Media Audio
Encoded date                             : UTC 2016-02-20 03:21:18
Tagged date                              : UTC 2016-02-20 03:21:28

The spl handling of phones and portables is also quite bad. Holding it in front of a speaker or monitor only makes matters worse. Uploading such footage is kind of risky.

It's possible (likely) that the iPhone 6 audio is distorting in Vegas Pro. Smartphones and many cameras use automatic gain control to maximize the loudness of the audio when recording. The AGC will run the volume right up to the maximum before clipping. I observed input meter clipping when I put Mono audio into a stereo Vegas Pro project. One way to avoid this is to change Pan Type of the audio track from Add Channels (0 db Center) to virtually anything else. In this video, I chose -6db since the audio was plenty loud already.

It pretty much has to do with the fact that you're trying to record with a telephone. As soon as you bring the sound from a telephone into a decent sound system all the flaws created by the telephone will be intensified.

Back up a page and post MediaInfo per the directions for both source and render. It will also be necessary for you to upload a sample of the footage from your phone to a legit file share site.

That said, I have never heard iPhone audio from a concert that "sounded fine," except on an iPhone ...

What is render? (told you I am new!)

When you "render" in Vegas Pro, you commit all your edits and save to a new file. None of your source files are changed, but rather you create a new file.

It's possible (likely) that the iPhone 6 audio is distorting in Vegas Pro. Smartphones and many cameras use automatic gain control to maximize the loudness of the audio when recording. The AGC will run the volume right up to the maximum before clipping. I observed input meter clipping when I put Mono audio into a stereo Vegas Pro project. One way to avoid this is to change Pan Type of the audio track from Add Channels (0 db Center) to virtually anything else. In this video, I chose -6db since the audio was plenty loud already.

 

Thanks I will try this. A question: if it sounds fine uploaded to Facebook...I do some edits in SVP (even if it sounds bad) and then upload again to FB...does this make sense? The final purpose is just to use this singer's video on FB.

Your Vegas edits should add value to the video clip, trimming to get rid of extraneous material, titles, color correction, volume level adjustment, etc, or they may not be justified if all you want is the spontaneous view of the performance. That said, you should be able to edit in Vegas Pro without making the output look and sound worse. Folks do it all the time, all over the world. Even I can do it so that means it must be possible for others.

If you get your audio to sound good in Vegas Pro, perhaps you could render to XAVC S Long GOP 1920x1080-29.97p. That render option uses LPCM lossless audio and your output won't suffer any further degradation from the encode in Vegas Pro. Get a good Internet connection as the files are large.

General
Complete name                            : C:\Users\John\Desktop\iPhone Audio\XAVC S Long 1920x1080-29.97p.MP4
Format                                   : XAVC
Codec ID                                 : XAVC (XAVC/mp42/isom)
File size                                : 68.0 MiB
Duration                                 : 10 s 577 ms
Overall bit rate                         : 53.9 Mb/s
Encoded date                             : UTC 2017-03-27 19:45:04
Tagged date                              : UTC 2017-03-27 19:45:04

Video
ID                                       : 2
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L4.1
Format settings, CABAC                   : Yes
Format settings, ReFrames                : 2 frames
Format settings, GOP                     : M=3, N=16
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 10 s 577 ms
Bit rate                                 : 52.4 Mb/s
Width                                    : 1 920 pixels
Height                                   : 1 080 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 29.970 (30000/1001) FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.843
Stream size                              : 66.1 MiB (97%)
Language                                 : English
Encoded date                             : UTC 2017-03-27 19:45:04
Tagged date                              : UTC 2017-03-27 19:45:04

Audio
ID                                       : 1
Format                                   : PCM
Format settings, Endianness              : Big
Format settings, Sign                    : Signed
Codec ID                                 : twos
Duration                                 : 10 s 560 ms
Bit rate mode                            : Constant
Bit rate                                 : 1 536 kb/s
Channel(s)                               : 2 channels
Sampling rate                            : 48.0 kHz
Bit depth                                : 16 bits
Stream size                              : 1.93 MiB (3%)
Language                                 : English
Encoded date                             : UTC 2017-03-27 19:45:04
Tagged date                              : UTC 2017-03-27 19:45:04

With any iPhone video, I would start by converting it from mov to mp4, to take Quicktime for Windows out of the scenario. It probably won't fix the audio by itself, but it's generally a good thing to do for iPhone video, in particular for smoother playback and corrected luminance (brightness/contrast) in Vegas.

If audio distortion is simply caused by the overloading you will see the audio waveform preview touching the top and bottom of the track and perhaps even get clipped ("cut off") at the peaks. For example, here's a mono track I recorded recently, zoomed in, with clipped audio:

There are some free plugins that attempt to repair such distortion. If this is really the issue, then one of these might help.

With any iPhone video, I would start by converting it from mov to mp4, to take Quicktime for Windows out of the scenario. It probably won't fix the audio by itself, but it's generally a good thing to do for iPhone video, in particular for smoother playback and corrected luminance (brightness/contrast) in Vegas.

If audio distortion is simply caused by the overloading you will see the audio waveform preview touching the top and bottom of the track and perhaps even get clipped ("cut off") at the peaks. For example, here's a mono track I recorded recently, zoomed in, with clipped audio:

There are some free plugins that attempt to repair such distortion. If this is really the issue, then one of these might help.

Hi..what is overloading? I think the problem is the sound coming from the performer's monitor onstage, heard on top of the vocal and guitar miked sounds. I"m just guessing...not a sound engineer lol.

Hi..what is overloading?

I mean the peak values exceeding 0dBFS (decibels). Devices with automatic gain compensation, like phones and many cameras, are designed to avoid that, but they may not always succeed.