Meh. It depends on who I'm at that table with. Tuesday night, I went to a biweekly potluck that my small group does. One of the girls had a birthday that night, so we had cupcakes and a round where everyone told a story about how they'd first met or interacted with her. Much laughter, much closeness, and much love. I'd've never dreamed of taking my phone out of its carrying case.
But last Sunday night, a friend of mine was having a sendoff. It was her last night before returning home to CA, so she invited me out with her and some friends from her bible study. Seriously, she was the only one at that table who even looked my way, much less talked to me. Once I gave up trying to be part of the conversation, I pulled my phone out and stayed on it until I left.
Politeness is a two-way street. If you're going to make a big deal out of somebody checking their phone at the table, try including them in the conversation first.