If you've created a group without assigning it a phone number or extension, you can easily add these later by following the steps below.
Go to Account Administration and choose Groups in the navigation bar.
Select the group for which you wish to assign a phone/extension numberOn the group’s page select Edit under Group routing. Click the + Phone Number or + Extension button.
A pop up box will appear which will allow you to choose the phone or extension number to assign to the group.
Important: If you select a phone number that is already assigned to a User or Group phone, the phone number will be removed from this User/Group and re-assigned.