My mac won't let me choose my phone number as an option. Last year, I had taken my phone number off and now I can not get it back. I tried creating a second Apple ID, I signed in and out multiple times and my number is still not there.
To specify your phone number as, say, a message address; you must set it up from the device that can actually be reached from that phone number. Your Mac is not such a device.
Once you have it set up, you can continue to use the phone number to send messages, and will be able to pick them up on your Mac.
See:
Link your iPhone number and Apple ID to use iMessage and FaceTime
As Grant says, you must have an iPhone using the same ID for FT and Messages
mac won't let me use phone number
