Your iPhone Is Overheating
All iPhones, new or old, will overheat from time to time. Of course, it’ll also depend on the way you use and charge your device.
With that said, older iPhones might overheat for no apparent reason. You might experience overheating while your iPhone is charging, even if you aren’t using it when it charges.
Not only is this an issue, but it can also damage your iPhone’s battery and hardware in the long run. If this is happening to you, upgrading your iPhone might be the best solution.