Avoid Using Your iPhone in Direct Sunlight
While it’s true that we as humans need some sun now and then to stay healthy, iPhones don’t work the same way.
As a matter of fact, according to Apple, iPhones are built to work best between 0º and 35ºC (32º to 95ºF). If you’re using your device in direct sunlight, especially for long periods of time, the internal temperature can rise pretty quickly.
This is common at the beach, pool, or if you leave your iPhone in a really hot car. Of course, sometimes you can’t avoid it, but you should try to keep your iPhone away from sunlight as much as possible. Not only will it make the screen hard to see, but it can also push your iPhone beyond the recommended temperature.
If your iPhone starts to feel hot in the sun, move it to a shaded area as soon as possible. Likewise, avoid placing it on heat-retaining surfaces like metal, glass, or asphalt. Let it cool before you continue using it.