I'm asked for two factor authentication, but I don't have this old phone number

See: Two-factor authentication for Apple ID - Apple Support

including the following from that link:

What if I can't access a trusted device or didn't receive a verification code?

If you're signing in and don’t have a trusted device handy that can display verification codes, you can have a code sent to your trusted phone number via text message or an automated phone call instead. Click Didn't Get a Code on the sign in screen and choose to send a code to your trusted phone number. You can also get a code directly from Settings on a trusted device. Learn how to get a verification code.

If you use iOS 11.3 or later on your iPhone, you might not need to enter a verification code. In some cases, your trusted phone number can be automatically verified in the background on your iPhone. It’s one less thing to do, and your account is still protected with two-factor authentication.

If you can’t sign in, access a trusted device, reset your password, or receive verification codes, you can request account recovery to regain access to your account. Account recovery is an automatic process designed to get you back in to your account as quickly as possible while denying access to anyone who might be pretending to be you. It might take a few days—or longer—depending on what specific account information you can provide to verify your identity.

If the 2FA is created from an iPhone and that is lost , and if you remember the trusted number say 1234... contact cellular service provider and issue a new sim using same mobile number ( you have to give some proofs of identification that you are only person who used that number to the service provider ) .

Take a new iPhone and insert that sim into it https://support.apple.com/en-in/HT201337

And set the new iPhone https://support.apple.com/en-in/guide/iphone/iph1fd7e482f/ios

Use the same Apple ID and password that remains same with your 2FA account ( you signed in your old lost iPhone ) , the code will come to this iPhone and you can sign in the 2FA account .

If you created 2FA from a Mac , open system preferences > click on Apple ID , again click on password and security , in front of trusted accounts , click on edit , click on plus sign and add your new trusted number and click on done , you can later delete the previous lost trusted number bu clicking on subtract sign .

The new number has to be verified .

Also you can click on get a verification code , a code will be generated write it down , open a new tab on the same Mac ( use command and T keys ) , sign with Apple ID and password at www.icloud.com the code is with you fill it up in the field and you will enter the 2FA account .