how to reset apple id password when then phone number is not avalable

Using your mobile number is just one of the ways to reset your password. In some cases it is just used to verify your identity and does not actually send a link to it. Other ways include sending a link to your Apple ID email address. You also have the ability to do it with a Trusted Device or other Trusted Phone number that was set up with the Apple ID. Without the Trusted Device and Trusted Phone number you will need to use the third option to start Account Recovery using the iforgot.com website. There are several steps to this that does not rely on just your phone number. The less information you are able to provide to verify your identity the longer it will take.

If you forgot your Apple ID password - Apple Support