Oh I have had to do the same with my DDs. I make them leave their mobile in another room when we are eating. They seem addicted to it.
I fully expect to be sitting at their dining table in 20 years time, with DDs, their DHs and my grandchildren all texting away. I will be wittering about how that wouldn't happen in my day and what is the world coming to.
YANBU. I don't mind people looking at a text or answering a call during mealtimes if it's important, but actively making texts/calls themselves comes across as very rude to me.
A large group of my family went to my grandmother's house for Christmas day, during lunchtime my uncle was actively on his phone, texting and laughing while staring at it. Needless to say he got an angry and disappointed look from myself, and my grandmother had raised her voice to say that she felt he was being disrespectful.
We allow it (well, DH and I use our iPhones, son is only 2!) if it is just the immediate family, just like we allow reading. However, the rule is if someone speaks, everyone puts down what they reading/looking at and engages.
We never do it if we have guests or are out in public.
The whole 'my mobile is far more important than real live people' problem is escalating. It's amazing how you can be in deep conversation with someone when the phone goes off and it's like a dog-whistle! They stop mid sentence, surprised look on their face, and start fishing around in bags and pockets, totally ignoring you. Sometimes even holding up a hand like a traffic cop. Chuckling at private texts or chatting away and miming who it is on the other end... like you give a damn! We spend an age teaching our DCs not to interrupt when someone's talking, and then this happens. Manners... window... drop-kick
In our house phones at the table are banned, with no exceptions. If I've taken the time and trouble to cook a meal then the least you can do is extend me the courtesy of eating it without implying that the whoever is on the phone is much more important.
Even MIL got told on Christmas Day once. FGS very little in life is that important that it can't wait for half an hour.