If the thing continues with that after it is good and cold, then there might have some degree of permanent damage, thus the need for repairs. These entail exchanging your phone for an identical refurbish of same characteristics, for the standard out-of-warranty cost. Had you purchased AppleCare+, would have been $80.
If you do go for the repairs, remember you'll be getting a blank phone, your stuff is your responsibility. So make a complete and reliable backup first so it can be restored as it was. Best is thru iTunes on a computer (Mac preferred), set to store locally on the drive, WITH PASSWORD. An iCloud backup is not as complete but still better than nothing.
Before handing the corpse over, do this so your privacy is preserved: What to do before you sell or give away your iPhone, iPad, or iPod touch - Apple Support