Keep in mind the screens on phones are LCDs; LIQUID Crystal Displays. The volume of the liquid expands by about 10% when it reaches freezing point. To be honest, its not very likely that it would crack if exposed to extreme cold for a short period of time, so its possible that it froze JUST RIGHT and busted the glass. Glass has a nasty habit of being unpredictable. It can take either massive pressure or very little pressure at the right angle to brake it.
The best suggestion is to always have it on you so it stays warm. It won't survive by itself in the cold
