Your example of calling the Mrs etc is fine, but many many people are on the phone for business / work reasons, which in many cases means their concentration is not on the road! its on the conversation.
True but even so, I don't think using a phone makes a good driver a bad one, nor does not using a phone make a bad driver a good one. I think it makes little difference. It's a small risk factor, comparable to having kids in the back, listening to loud music or carrying an irritating passenger.