What is the maximum temperature an iPhone can withstand

Hey there,

Surely your phone will be hot if it is exposed to the sun. See ☞ If your iPhone, iPad, or iPod touch gets too hot or too cold - Apple Support

The tech specs for an iPhone or iPad will list this information.

Here is iPhone 13:

Excessive temperatures will degrade batteries.

Yes, that's how physics works.

Anything gets hot when left in the sun, including the human body.