She probably tried to convince him that her phone was actually his father.
Nag, I believe the proper course of action is to take her phone and simply throw it on the ground. This sends the message that both your dad's not a phone and that you will not take part in her system. I heard of a guy with the same problem, and this is how he handled it. As far as I know, it worked out really well!
Anyway, good luck.