I thought about doing this, but considering I can hardly see my screen in direct sunlight, I doubted it would be very useful pointing straight up at the sun while cycling! I have a Samsung however, perhaps that iPhone is a bit better, but here is what I am talking about:
https://www.youtube.com/watch?v=zqnosPs1_zo

Other issues will include battery life when you switch the screen to "always on at full brightness". Probably no more than an hour when fully charged, and then you have a dead phone after your ride.