I see plenty of senior staff members, well and truly over-the-hill types, who are just as bad about using their phones in meetings. 20 somethings are going to take their lead on how to act in a meeting from their peers. If you clearly set an example of what is OK and not OK in a meeting, this isn't a problem but many Managers don't bother to manage. Do yourself a favor and don't bring your phone into a meeting, at all. If you really MUST be connected, weight what is more important to your personal reputation at that moment. Disrupting the meeting and taking a communication, or realizing part of your job is to be fully committed to the place you're at.