I find it bizarre and indefensible both that your T would use or pay attention to her phone during your session, and that she would be personally offended by your mentioning this.

I thought the way Pennster phrased it above was very polite and not accusing at all. I would try that approach. If it doesn't work, ditto those people who said to find a new therapist, because why on earth would anyone pay money to watch her fiddle with her phone.