Apple iPhone 16e gets hot or shows a temperature warning

The checks in more detail

A new phone in particular does a day or two of background work after a restore, so a phone that is warm and drains fast on its first day usually settles down. Heat is not normal when the phone is warm at rest with the screen off, when it shows a temperature warning, or when it is hot enough that the screen dims and the camera or flashlight is disabled, because the phone is protecting itself. For those cases work through the causes.

Take off the case and remove the phone from direct sun or a hot car, since the case traps heat and ambient temperature matters more than anything. Stop charging for a while: wireless or fast charging produces heat, and charging while gaming doubles it. Look at Settings, Battery for the apps using the most, and force-close an app that runs hot, or update it. Check Background App Refresh and location settings for apps that run constantly. A weak cellular signal makes the modem work harder, so connect to Wi-Fi or switch to Airplane mode for a test;

the C1 modem is efficient, but a poor signal is a classic heat source. Restart the phone and install the latest iOS, since Apple tunes thermal behavior in updates. If the phone is still hot at idle with a good signal, no case and a clean restart, back up and see whether a clean install helps, and if it does not, Apple can test the battery and board. A phone that swells, smells hot or shows a battery warning needs service at once, and should not be charged.