Press the up or down buttons just under your display to adjust handset volume or speaker volume, depending on what you are using.
On ESI digital phone models dPhone4, 55D and 60D: To adjust the ring volume or change the ring tone, press PROG/HELP or HELP. Then press 4 for station audibles, and 1 to change the tone or 2 to adjust ring volume.
On ESI IP phone models, press the volume up or down when the phone is idle to adjust ring volume.