Up until recent updates the mobile application had a setting toggle for 'Silence Incoming Calls.' By default when first signing into the application for all users it was turned on, but could be toggled off so you would have all calls ring on the device.
However, after recent updates the extensions role must have permissions (User Settings > Messages & Notifications OR Call Handling/Forwarding) allowed in order for this setting to appear. It seems that oftentimes this feature is still toggled on by default when a user first downloads and signs into the mobile app. An admin has to update the users role temporarily just to turn off the toggle so calls can ring through on their device.
This seems like an oversight, but would be HUGE for our entire organization if this setting were to be reinstated.