I currently have a P3S and am connecting via an Andriod phone running DJI GO v3.1.3.  The A/C is at v1.8.10 and I'm using a 64GB SD Extreme card in the camera.  I have a new phone on order (iPhone 7 Plus 256GB) so when it arrives I'll need to swap to the IOS version of DJI GO.  The phone part seems pretty obvious (new phone - download new version), but I'm wonder if any changes might be needed to the A/C itself.  Specifically I'm wondering if I'll need to format the SD card, or will I need to follow some specific order, etc.  Appreaciate any advise.

You won't need to change anything on the Phantom.

Thanks Labroides!  Was hoping it would be an easy swap.