Your phones are configured to adjust the volume of both the ring and speaker when on a call. Follow the steps below to adjust these two types of volume control.
Adjust ringer volume
Press the left or right arrows when the handset is idle
Press the save soft key to accept the change or the back soft key to cancel
Adjust the call volume
While on a call, press the left or right arrows to adjust the volume of the currently engaged audio devices (handset, earpiece, headset, or loudspeaker)