Hi my name is ***** ***** I can assist. Yahoo will not allow you to change the phone number on the security settings without having access to the account as it would circumvent the security in place. Have you tried accessing it your Yahoo account with the security questions?
If you've set up the alternate e-mail address, that would work too.
Let me know if you need any more help, I'll leave the ticket open for your response. If I was able to answer your question, please rate my service with the stars above with 3 stars or higher if I was able to provide you with excellent service. Otherwise, I will continue to work on your issue until you are satisfied.
It seems there may have been issues getting my responses to you. I just want to make sure that you received my messages and to see if you still need help