Should I replace her phone?

So my grandmother offered to watch my son while I get a nap since he was up all night. I got about a half an hour nap which I'm so thankful for but she had let my son play with her phone while I was asleep (which I did not know about). Now she is claiming that I should replace her phone or pay to have it fixed because my son had ruined her speaker. I never let my son use electronics and he had plenty of toys all over the room including a jumper, an exersaucer, and a play mat along with it. She let my son chew on her phone and now the speaker is ruined, which was not my choice for her to give to my son the phone in the first place. I am very grateful that she watched him for a short time but should I have to replace her phone because she let my son play with it? (She knows he is teething and drools everywhere and brags about her grand baby teething all of the time). I'm stuck in this position and don't really know what I should do. I never asked her to watch him, she offered so I let her.