Please make sure that you have set up your VoIP extension line number inside the Settings - Your Settings tab - Click2Call field.
Now go to the contact record and click on the Mobile number a pop up window will appear.
Click on call icon (as shown below) and the number will automatically dial your phone handset or softphone.
Press the green key to connect to the outgoing call (as shown below).
If you require assistance please contact our Support Helpdesk.