Adding the UCP Phone in UCP
The UCP Phone widget is only available as a Side Bar Widget.

Once added the phone will show up on all dashboards to the left.

Clicking the phone will bring up the dialpad. You can receive calls even when the dialpad is closed.

You can type a number into the interface and then click call to place a call.

Calls can be placed on hold by pressing the hold button:

if you close the window will in the middle of a call the call will stay connected and a countdown timer will be added to the side bar icon:

UCP Phone Settings
You can set specific settings for your phone in UCP by clicking the gear icon:  

Silence Ringer: Silence the ringer for inbound calls.

Disconnect Phone: Disconnect the UCP Phone. (appear as offline)