high temperature message

Hello,

If you see a temperature warning screen

If the device exceeds a certain temperature threshold, it will present a temperature warning screen similar to this:

An iPhone showing this message might still be able to make emergency calls.

To resume use of your device as quickly as possible, turn it off, move it to a cooler environment, and allow it to cool down.

More info here:

Keeping iPhone, iPad, and iPod touch within acceptable operating temperatures - Apple Support

When you see this message, it means the iPhone is already protecting itself from damage. All you need to do is allow it to cool down. You might want to keep an eye on how hot it's getting and give it a rest before it shuts down at possible very inopportune times.