All Vegas video dimensions are in multiples (modulus) of two. If not, the encoder adds a row of pixels. Your iPhone will look great at 1124 or 1126. Also at 1080p. Stills can be odd dimensions.
Trivia fact: In the early days of video, all dimensions had to be in multiples of four. Some AVI and MOV encoders still require this.
I don't know of any video software that will make 1125 vertical pixels. Check with your app vendor for the requirements, or check other's work using MediaInfo.
1126p mod 2 is the default convention for what you are trying to do.For example only, NTSC Widescreen is 854 square pixels wide, not 853.333_.