Overheating iPhones has been an issue on and off for years. Sometimes there are obvious reasons for overheating like leaving your iPhone in a hot car or taking it to the hot tub. However, most overheating issues usually involve either Software or possibly Hardware problems on the phone. You may not be experiencing this problem right now, but it is a good idea to read this article which describes things that cause an iPhone to overheat and ways to resolve this problem. The article is quite thorough. Some of the fixes are a bit drastic, but if nothing else works, they would be your last resort.