"She seems to have suggested that a party host collect people's cell phones, like coats. "
That struck me as odd as well. Talk about a host acting like a control freak... I'd really question whether or not I'd really want to be in the home of someone who insists on taking personal items from me. The host is basically saying "Ok, you are all rude childish boors, and if you cannot control yourselves, I'll do it for you". Its not like answering a quick call at a party is terribly rude anyway, I mean, what about people who have children home with babysitters?