I agree, however the mom is just trying to protect her child, yes it may seem like disrespect. But wouldn't you do the same for your child. People kill and die to protect their children, her going at your phone is nothing to that degree so be glad.
You might also might come off to the mother that you are the kind of person that would endanger her child.
Me and my Gf's parents get along great, because I give them the peice of mind that their child will be safe with me and that I will do all in my power to protect her, when shes away from home. Maybe you should focus some effort into talking to her mother yourself and give her some comfort that you repect her wishes and what she want to do with her child. I know I would "protect" my child if some punk kid ( not saying your a punk, just that is how alot of parents see boys dating their child now adays) Sounds like you try hard to get along and that you are a nice kid, but trust me don't let it get to your head. THe mom has problems with you, thats her problem not yours, so don't let it bother you that much if you know that what she is looking for is not there.