I tested shooting photos and video by zooming to like 2.5x with DJI GO app, and compared with the same zoom ratio with stock camera app in IOS. The result shows that the DJI GO app can is obvious appling digital zoom on the wide-angle camera instead of applying the telephoto camera. Tested on my iPhone X, so I guess this should be the same with the iPhone 8 Plus and iPhone 7 Plus. Please consider add support to the telephoto camera in the DJI GO.

Thanks for your attention and feedback. Please note that the use of double camera can not be adjusted in the app. Iphone X will adjust the camera according to the environment.