While the phone is idle or ringing, you can adjust the ringer volume. When the phone is connected to a call you can adjust the speaker or handset volume.
To Adjust the Ringer Volume
1.Use the 
up arrow and 
down arrow keys to change the ringer volume.
To Adjust the Caller Volume
The volume that gets adjusted will depend on whether you are using the handset or speakerphone at the time you use this process.
1.Use the up arrow and down arrow keys to change the volume.