I have yet to use my iPhone for the burning process. Since all you want is to make a video DVD I'll lead with the free and on the web documented http://www.dvdstyler.org/en/
I'm sure there are dozens more free titles out there but since how to use is on the web, I stop here.
I am looking for DVD burning software that will burn videos from my iPhone 6 and will play on an XBox. The videos are saved on my PC.