My friend recently left his iPhone out in the sun while swimming at the pool. When he came back, his iPhone was locked with the message "iPhone needs to cool down before you can use it."
Neither of us had ever seen this warning before, despite leaving our phones out in the open before.
How hot does an iPhone need to be before displaying a high temperature warning?
Best Answer
TL:DR - Don't leave it in the sun. Especially face up with the black display (and pobssibly bezel) exposed to direct sunlight.
From Apple KB: