The company I work for does a lot of high end database and program management discussions. In our meeting rooms have Faraday case/box where we place our phones if we bring them with us. Blocks all signals. You can buy small Faraday cases for your phone for cheap.

Found it on Amazon: https://www.amazon.com/Black-Hole-Faraday-Duffel-Bag/dp/B00EKPKB5U/ref=sr_1_11?ie=UTF8&qid=1482956331&sr=8-11&keywords=Faraday+case