GreatCall Jitterbug5 User Manual page 61

NOTE:
The selected volume level will appear on the Inside Display. The Ringer
Volume cannot be adjusted while actively on a call.
The ringer can be silenced by pressing the volume button down until
"Vibrate" appears on the Inside Display. With "Vibrate" selected your
Jitterbug will only vibrate to alert you of incoming calls. This can come in
handy at a movie, a library or any other location where a ringer may be a
distraction.
52 Placing And Receiving Calls