This will hopefully help give you a base for filming with cell phones as the camera.
The only real setting needed is that your iPhone be in 4K 24fps. It's under:
SETTINGS > CAMERA > RECORD VIDEO
This is a great example of how to frame the subject.
A little room over their heads and capture down to their knees. Try to hide the mic cable behind them and under clothing. * BE SURE THE PHONE IS HORIZONTAL, not verticle.
Make sure you're in "video".
Just press record once before you start and again when you finish - we will edit out the questions and everything in between. The entire interview should be 1 video file.
The main point is to conceal the wire. It should run under their shirt, inside a jacket, etc...
The microphone doesn't need any settings. If it is plugged into the phone's lightning port, it will record.