Someone who sounds like your mother, either in vocal quality, mannerism, or content. (Etymology: A quasi-homophone of homophone.)
Caller: Hello, is John there?
John: Yeah, it's me, Mom.
Caller: Actually, this is Janice from AT&T. Would you like to upgrade your service? We're offering a special to people in your area.
John: <hangs up> Dang, I was tricked by that mamaphone!
Girlfriend: Frank, be back here by 7. No excuses.
Frank: Yes, dear.
Frank's bro: Dude, your mamaphone girlfriend just set you a curfew!