I'm currently sitting here in the U.K., which is currently undergoing a monster heat wave with temperatures expected to exceed 100-degrees Fahrenheit later in the week. Needless to say, staying cool has been a priority, not just for me but for my phone as well.
Just like people, the best phones don't do so well in extreme temperatures. Batteries, in particular, are more prone to degradation when things get too hot, but temperatures like this can cause all sorts of problems, from overheating to damaged screens.