I often fly Spark with my iPad 6 so I can see what I’m shooting and all the telemetry etc. But, have been using my iPhone 6s recently and get on well with it.
Since I'm not an Apple guy and not sure how the performance of some of the products operate, I did a quick check.
The DJI FLY app that flies the MA2 requires a 64 bit operating system and it looks like you're good to go with the app on both devices

There have been threads about switching from the Go4 to the Go Fly and the users finding out that the devices aren't compatible.

Although, there's some chatter on the Mavic site about the Go FLY app and it's operating system that is overheating some the apple products that causes the display to become dim when flying, which is useless.
Some of the remedies are to take it out of the case, airplane mode, etc. and find shade if possible.
Low Power mode and Do Not Disturb turned ON seems to help with the DJI 1.4.8 version and the Apples.
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