As a Driving Instructor unfortunately this is something I see on a daily basis.
People using the mobile phone in all sorts of situation, but I have seen other things as well, lorry driver with a can of pop in one hand sandwich in other.
I have seen ladies putting make up on in rear view mirror, plus loads more I could talk about.
Sat nav 4 out of 5 driving tests now use it for approx. 20 minutes on test. Modern Way ? Other one is following signs or directions for a certain place, this is the independent drive section, basically can they think and decide for themselves.
One thing to have in mind, is the phone on show? put it somewhere where you cant reach or see, glove box, bag in back.
If it rings pull over and switch engine off before answering...…...if its really important and you miss the call I am sure they will ring back or wait till you return call.