Hii

I dont think AIIMS code generation has anything to do with the Phone number.
You simply need to login to your basic registration form on the following link - http://ugcourses.aiimsexams.org/#!

Enter your registration id and password and after logging in to your account, you will lfind a link on the left hand side of the page CODE GENERATION. Click on this link, select the examination as MBBS and click on generate the code.
Your code will be generated and you can proceed to the final registration on the following link - http://mbbs.aiimsexams.org/

Hope this helps
Thanks!