Why does my iPhone get hot then sometimes freezes?
Why does my iPhone gets hot and then other times will freeze until I reboot it?
iPhone 6
May have a defective battery or other hardware issues. Best to have an Apple Store test it. You could try the steps below to exclude software concerns. They may help if it is iOS related.
Try holding down the Home and Wake/Sleep buttons at the same time for about 15 seconds until the Apple logo appears. You will not lose anything.
If a restart does not help try a System Restore. First backup your device using iTunes. Also import your photos to your computer and copy all important data if possible. Try restoring from backup first and testing it. If it does not help, you may have to restore as New and reconfigure from scratch as the backup could be corrupted. For this reason it is important to have your photos and data saved separately from the backup. Here are the steps for a Restore: