If all you hear are strange, muffled noises, chances are it’s a pocket call.
pocket call
/ ˈpɒkᵻt ˌkɔl / nouna call that you make by pressing your phone by accident:
It must be a pocket call – I can’t understand a thing.The verb is pocket-dial or pocket-call:
It can be embarrassing if you pocket-dial your boss from the bar.Read all about it: Will smartphones take over the world?