From what i know, you cannot use phone number that was not added as recovery phone number previously.

The only way is to use the secondary e-mail that was compulsory added when creating the gmail account. This is your only hope really.

There might be a possibility to recover if you have an android phone that has a google account and you could add this email as an account inside. But i have not tested this yet.

If anyone could just add a random number to take claim of the gmail acc, then its a pointless security measure no?