It's about an iPhone, what should I do?

So myoms iPhone was working at dinner (1 hour ago) and then we went to get something from the store and now he phone just won't turn on, we've plugged I in we've called it, do you know wa to do?

Plug it in and leave it on charge for a little, it might be dead. If that doesn't work than just turn it on by holdin down the lock button, and if that doesn't work, its damaged