New ipad won't let me enter correct phone # for imessage

I bought a new ipad gen6. My wife and I share the same apple ID. The apple ID is my email address and has my phone number as both the "reachable at" and "trusted" phone number in the ID profile. My phone has my email as the Apple ID and the "You can receive messages to and reply from:..." lists my phone number. I used my phone to pair with the new ipad during set up. On the ipad, under settings/messages/You can receive imessages to and reply from....it lists my email, and my wife's phone number. It will not let you delete and re-enter a different number. You have the option of checking it...or not checking it. Any ideas how to enter my phone number here in order to be able to use the ipad for imessage?