why does iPhone get hot when being used

Hello josephfrompuyallup,

Based on the information that discusses iPhone temperature found at If your iPhone or iPad gets too hot or too cold - Apple Support:

Your device might get warm

You might notice that your device feels warmer when you:

* Set up your device the first time

* Restore from a backup

* Wirelessly charge your device

* Use graphics-intensive or processor-intensive apps, games, or features, including augmented-reality apps

* Stream high-quality video

These conditions are normal, and your device will return to a regular temperature when the process is complete or when you finish your activity. If your device doesn't display a temperature warning, you can keep using your device.

There is also information on that page that provides steps on what to do if your device gets too warm.

Cheers.

Joule’s 1st Law (et al.) and inefficiency.