You can laugh my phones packed up more than once in the heat.
They have battery protection so if it gets too hot they go into a type of low power mode to reduce the battery temp, the screen dims to the lowest setting, refresh and background activity is stopped.
Only happens in direct sunlight, using satnav and charging it at the same time. Got lost for over an hour thanks to that.
Went into a cafe and got some ice put it in a bag and wedged it behind the phone holder, worked a treat.
by the way phones silicone cases can increase this heat, silicone is made from sand, its a complex process involving many stages, have I told you about sand yet? I understand @Bucksters keen to know.