Your iPhone 5 is not up to the task. You'll need at least an iPhone 5S. This quote is from DJI site...
My final question is this: Is the iPhone 5 not powerful enough to run the DJI GO app?
"Requires iOS 8.0 or later. Compatible with iPhone 5s, iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus,iPod touch 6,iPad Pro, iPad Air, iPad Air Wi-Fi + Cellular, iPad mini 2, iPad mini 2 Wi-Fi + Cellular, iPad Air 2, iPad Air 2 Wi-Fi + Cellular, iPad mini 3, and iPad mini 3 Wi-Fi + Cellular."