From reading on this site, what you are experiencing would be known as a **** test, which is a test that women pull by acting rude toward you, to see if you are a real man and would stand for it.
If you guys are talking and her phone rings, if her interest level is high she will say, call me back or turn her phone off. If she is bored or her interest level is low, she would use talking on the cell phone as a way to escape her current dinner date. My question to you is, and I dont mean to be harsh, dont take it that way, But....WHY THE HELL ARE YOU AT A DINNER DATE?????
ONLY ACTION DATES MY FRIEND!! No romantic candle light dinners. If you are hungry, go through drive thru, and you pay yours and she pay hers (something I get her to pay both, hehe).
My overall opinion was that she was bored and she used the cell phone as a way of saying that. I am quite sure whoever she was talking to was not talking about ****. And you say, should you say something to her, like get off the phone!!! Well, my friend, if you were on an action date, she would not even have her cell phone on. You got me.