exploded iPhone

I have an older iPhone (a 3gs I believe) that I use as an iPod in my Jeep. Yesterday I jumped in and noticed there was no music; I opened the center compartment and found my iPhone's insides had expanded to the point of popping the screen off the body at the top. Picture attached. While we have had a couple of freezes here over the last couple of weeks, it hasn't been that bad. What would it take to cause damage like this?

Did you check to see if the battery had expanded or exploded? That might be what caused it.

Prolonged exposure to high heat. Like say keeping it in a center compartment on sunny days with the windows rolled up for example.

I am going with chas on this nothing says greenhouse affect like a closed up auto in sunlight.