I got a bit upset with a fellow regular at my local shop's casual boardgaming night. Just about every time he will have his smartphone out while we are playing (Terra Mystica was what was up that night), grinding whatever phone game he was on between turns. And often had to be told it was his turn.
When I suggested (perhaps a bit shortly) he pay more attention to the game on the table, he got short with me later, asking if we were penalizing people for taking long turns when I was trying to figure out my best move.
So playing on your phone during a game. Always rude, only okay if there is a long gap between turns, or you are out waiting for everyone else to finish the turn, or fine if you don't have to be reminded too often or take too long to get back to the non-electronic game?