I first flew with the iPhone 6, but migrated to the 7+ for bigger screen and battery.
I've been very happy with it and never need to see more than I already see.
My only concern is that in bright sunlight, seeing details is an issue, but strangely I'm not in that situation often.
I also got some Android tablets for the purpose of using larger screens, but everyone here complains about the reliability of the Andriod DJI app, so I am afraid to even use it. I guess if I can't get buy with the 7+ and maybe a sun shade, I'll look for an iPad mini.