I'm not familiar with iPhones, but I am intimately familiar with stripped screws. Depending on how big that screw is, you may be able to remove it with an "easy-out." I believe they may also get wordy with the descriptions and call them something ridiculous like "stripped bolt extractors." Usually the process involves predrilling the center of the screw and then inserting the easy-out into the hole. Step2: twist out, Step 3: Profit.
Try looking at major tool distributers like MSCDirect.com or just googling "easy-out." If you can't find one small enough, try finding a small LEFT-HANDED drill bit. This drill bit twists the opposite direction, so it should be able to grab that screw and twist it out.
Sadly, small tools tend to be as expensive as really big tools. That said, you might get lucky.