Just to clarify. You'd like you desk phone to login to Extension Mobility after you login to your PC?
If yes, then there is no such a feature on CUCM. Technically this can be done with some 3rd party applications - I don't know if any companies offer such solution. But there needs to be a mapping somewhere to user <> phone.
Technically it's fairly simple to be done. For example you can add bat script to your PC that would trigger web-access in the background that would open: