I always leave my phone on in case of an emergency call from my mom but other than that I've never had to check my phone in a session before but once in 2011 when it was an emergency. I've had guys who keep their phones on and answer calls because of their work and it doesn't bother me if guys do it. Shit happens! But yea I agree that girls shouldn't text during appointments unless its a dire emergency and in which then they should not count that as the guys time.
Only time I see it being okay is during the overnight, all day and multi-day sessions.
Providers texting during sessions 3 hours or less is very unprofessional.
When the girl asks you what you like that's the time to say I don't like it when girls text while I'm going down on them. Ask at the beginning of the session that the phone goes silent. If they can't agree to that then walk and let everyone on the board know. If you don't ask for certain things then you probably won't get them.