When one acts like a completely different person to who they really are when talking to someone on the phone i.e. their parents.
Guy 1: "Hey dude should we go to that bar tonight and get blazed?
Guy 2: "Hell yeah!"
Guy 1: "Oh shit it's my mom. (Answers phone) - Hey mommy, ya everything is just fine, I'm just at the movies with a friend. I'll see you later. Love you."
Guy 2: "Dude, you are totally a phone skitzophrenic."