Apple® iPhone® - Turn Silent Mode On / Off

From the top left edge of the device, slide the Ringer switch to turn Silent Mode on (sound is off, the switch is in red position) Ringer on or off Ringer off.
Note The silent mode/ringer notification briefly appears on the screen.
Note If the switch appears to be stuck, remove the case to ensure the switch isn't blocked.
Silent mode switch


Note For more info on adjusting sounds and vibrations, check out this Apple Support page.