Re: why does my apple iphone 5c overheat so fast?
Welcome to iMore!
I do a lot of things on my iPhone while it's charging and it never gets warm. Are you playing games when it's charging? If so it depends on how warm it's getting. If the battery gets too warm it will shut itself down. I'm not sure about the CPU in iPhones, but I know on Androids the phone will shut down if the CPU gets too warm.
If you feel that it's getting unusually warm then take it into the Apple store where someone at the Genius Bar can assist you, or tell you weather or not you need to see an authorized Apple repair technician.