Keep Your iPhone at the Right Temperature
Your iPhone is smart enough to know when the environment is too hot to charge. If your iPhone starts overheating, it’ll either slow down its charging or stop completely.
Try to charge your iPhone in a room where the temperature isn’t too high. Likewise, take your iPhone out of the case if it’s making it too hot to charge. And, of course, as try not to use your phone as it charges because that will also make it hot.