Your phone generates relatively less heat when you make phone calls and send messages with normal signal reception and more heat when you take photos or shoot videos, play games that consume much battery power, surf the Internet, and download images or files. If your phone generates excessive heat at a certain time or during standby time, some applications in your phone are consuming extra battery power. Restart your phone and check whether this problem persists. You can also back up important data and restore your phone to its factory settings.