To call someone on the telephone. The phrase originates from the silent vibration mode on most cell phones. When the phone rings, your pocket vibrates.
1) I was like 2 fuckin thrusts away from nutting in her ass then some motherfucker started vibin' on my pocket and I lost my wood. It was fuckin' Clarence! I'ma ice that motherfucker.
2) Why excuse me sir. I believe someone is vibing on your pocket. It might behoove you to answer it.