If all you hear are strange, muffled noises, chances are it’s a butt call.

butt call

/ ˈbʌt kɔl / noun

an informal word for a call that you make by pressing your phone by accident:
It must be a butt call – I can’t understand a thing.

The verb is butt-dial or butt-call:
It can be embarrassing if you butt-dial your boss from the bar.

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