I've seen this complaint a few times with iPhone users. I don't have my P3 yet but going through the Pilot App on my iPhone 5s I've notice you can disable "Video Cache" to your device. (Personallly I don't see a real need for the phone to cache the video as long as the on P3 SD card is recording the video.) In theory having this turned off should increase battery life by lessening the work the phone is having to do. Therefore it also shouldn't run as "hot."

Has anyone tried this? Not having the quad yet to test, didn't know if there's a real reason to want my device to cache video other than as a back up?

Any thoughts?

Is that why my iPhone drains its battery so quickly? lol

The iPhone 5 has overheating issues in general.  If you run most processor intensive games the iPhone 5 gets hot & draws too much power.  It's not a DJI problem... It's an iPhone 5 issue.  The DJI app just uses a lot of processor resources.  The iPhone 6 does not have the same issues.

My iPad Air 2 works very well.  (But it's kinda big.)