What Robus said....it might be good to set some ground rules for gameplay before the session starts that everyone can agree to. Me and my friends are a bit older, most are married have kids, we dont get to D&D as often as we'd like so when we do, we are there to play. But, yeah, putting phones away would be a good start. Common courtesy. As the DM, I also request that my players come prepared with character sheets updated, please be familiar with your common attacks, bonuses and damage dice, and if you're a spell-cater to know your spells. We don't put timers on anything, but if it gets out of hand that's not a terrible idea. Then again, I'm lucky that the gamers in my group are all pretty mature and generally respectful. If your group isn't like that then yeah, you'll have to come up with something creative to manage the flow of the game or find a new group. Good luck.