Not letting me use phone number instead of email on FaceTime and iMessages.

its not letting me use my phone number instead of my email on imessages and telephone , i tried clicking the phone number but it either does nothing or shows as an unsuccessfull activation and because of that i cant really call anyone with my phone number. I also tried signing out and in of my iCloud but still nothing I tried many methods such as switching off and on WiFi etc… still nothing