Improve UX when incoming phone call is answered

[Alton09]

Is your feature request related to a problem? Please describe.
As reported in issue #87 and #76, we should provide a better user experience for handling an incoming phone call while in a video room.

Describe the solution you'd like
After looking at a few other collaboration apps that handle this scenario, we've decided to exit the video room as a solution to this problem.

Additional context
(Internal only) JIRA Ticket