OMG Amy, I should move cross country for your rates!
I have to agree. Amy's rates can not be beat. Around us it is $40 or $50 per half hour depending on who you go to. DD's had a coach who was $0 per half hour and she did occasionally get a text she would deal with durring lessons but that was the execption rather than the rule and if her prior lesson went over by a few minutes and DD started late because of it, DD always got to say a few extra minutes at the end to make it up. Generally the only time a pror lesson would go over if prior lesson was working on a new pitch that she was "close" to getting and PC didn't want to leave off half way.
But to the OP I agree with Amy, text her durring lessons something like - Hey my DD is paying a fortune for lessons and her PC is on the smart phone texting. What should we do?
Oh and then find a new PC.