I can’t connect my phone number to my iMessage or FaceTime. An error message is appearing

Hello Clairehyde88,

Welcome to Apple Support Communities. 

We understand that you would like to add your phone number to FaceTime and iMessage. We are happy to help.

These steps may help. Please try the steps here: Add or remove your phone number in Messages or FaceTime - Apple Support

"Set up your phone number

On your iPhone:

1. Go to Settings > Messages and make sure that iMessage is on. You might need to wait a moment for it to activate.
2. Tap Send & Receive. If you see “Use your Apple ID for iMessage,” tap it and sign in with the same Apple ID that you use on your Mac, iPad, and iPod touch.
3. In the "You can receive iMessages to and Reply From" section, make sure that your phone number and Apple ID are selected.
4. Go to Settings > FaceTime and make sure that your phone number and Apple ID are selected in the "You can be reached by FaceTime at" section.

On your other devices, you can now turn on the phone number that you just set up:

• Turn on your phone number for your Mac
• Turn on your phone number for your iPad or iPod touch"

Let us know if you have further questions.

Take care.