In the one year I saw my T, her phone was ALWAYS face-down on her desk, and I never heard it ring or vibrate. She used it ONE TIME, and it was because we were discussing the location of my new job, and she looked it up on her phone's maps app.
I really appreciated that she never used her phone. Even if she had just used it to check the time, I would have been nervous that she was quickly reading a text or something. Instead she used her watch and a clock.