...
You can set the default ring volume override to be used on your phone on a per-extension basis from within the Extension Page of your PBX.
Go into Extension Module in your PBX and select the Advanced Tab at the top
Scroll to Ringer Volume Override option and pick from volume levels 1 thru 14
Click the Submit button.
Click the Apply Config button.
...
You can set the ring volume override to be used for each of the following places in your PBX. This will override the default ring volume of the phone and replace it with the setting your choose here for the call flowing through the chosen destination only.
Directory
Follow Me
Inbound Routes
Parking
Queues
Ring Group
IVR
Navigate to the settings for the destination in the PBX GUI (for example, the specific directory, follow-me, etc.).
Change Alert Info field to one of the ring tone options shown below.
...
Click the Submit button.
Click the Apply Config button.
...