My mum is crying hysterically on the phone to my nan what do i do?

When she gets off the phone talk to her, hug her, tell her you feel bad that she is feeling bad. sometimes having a shoulder to cry on is always a good thing, its always a good thing to talk to another person so the person crying would feel alot better about her/himself and they can let out everything and anything that is bothering them. Hope all is well