Hi ,
I'm Dyari. Thanks for reaching out.
Just to clarify first, you won’t be able to sign in and change the phone number unless you successfully pass the verification process. In addition to the steps already provided, please check if you’re still signed in anywhere. If yes, go immediately to Security > Advanced security options and update your phone number.
Then, try any other verification methods you may have set up such as an authenticator app or backup email.
When using the recovery form, use a familiar device and network. Provide as much accurate detail as possible and avoid blank answers. If your request is rejected, wait a few hours and try again with more precise information.