Provision a new phone and Replace an existing phone:- its a new feature called phone migration.
If you add the phones manually, Make sure you selected correct device type and added correct Mac address with a DN assigned. make sure you configured Option 150 which is your TFTP server IP address. And make sure that on phone settings its showing the correct TFTP address.
If you are not adding the phone manually, make sure you have auto provisions enabled on your CUCM.