I want to make my mom quit playing Pokemon Go
Why do you want your mom to quit Pokemon Go?
I want to get her off the phone because it sucks
It is understandable that you do not want your mom playing Pokemon Go and always being on her phone, but it is wrong to tell your parents what to do. Thus it is rude to tell her to stop playing. But you should talk to her and tell her you have concerns about the amount of time she spends on her phone.
It's not that big of an issue.
Well still, I think you should have a conversation with her if her phone habits are bothering you. Otherwise you should let her do what makes her happy.