Unable to reset my Apple Account password using a new phone number

Then you need to use account recovery:

How to use account recovery when you can’t reset your Apple Account password - Apple Support

If you are unable to start account recovery you can also:

Contact Apple for support and service - Apple Support

The best option is if you have access to a trusted device, and can change your phone number and password from there.

Two-factor authentication for Apple Account - Apple Support

If you forgot your Apple Account password - Apple Support

If that does not work, you can start account recovery:

How to use account recovery when you can’t reset your Apple Account password - Apple Support

As long as you remember your old phone number, you can select that you no logner have access to it.

As long as you have access to an apple device, make sure you start the recovery from settings on that device (make sure if you start it from one device, do not use any other devices, turn them off until recovery is completed(they can cancel the recovery))