You probably need to go into Users and Services, then Network Element, and disable "Single Point Provisioning".
Then you should be able to go back into Users, and add the deskphone to the actual user. If you've already created the personal ring group and desk-monitor, you can also add the UC Moblie service now too. If you haven't seperately created the personal ring group & desk monitor, go back into Network Elements and re-enable Single Point Provisioning.