Go to https://settings.webex.com and select Webex Calling.
From the Calling User Portal, click Call Settings.
Toggle on Do Not Disturb.
Check Use ring reminder, to be notified by a sound when a call comes in.
Calling User Portal | Silence Incoming Calls to Your Phone
If you're busy and don't want to be disturbed, you can silence incoming calls with the do not disturb feature. When enabled, callers hear the busy treatment. You can also enable a ring reminder to play a brief tone on your desktop phone when you receive an incoming call while on do not disturb.