I'm sorry to hear that you're having trouble accessing your Microsoft account. To better understand the situation and help you find the appropriate solution, could you please clarify a few things?
When you try to sign in at https://account.microsoft.com using your regular password, do you receive an error stating that the password is incorrect, or are you able to enter your password but get stuck at the verification step? When you attempt to verify your identity using your phone number, what exact error message appears that prevents you from using it as a verification method? Since you mentioned having two-step verification enabled, do you have another verification method registered, such as an alternate email address or the Microsoft Authenticator app? If so, have you tried using it?
As you mentioned, phone numbers can change over time. This is precisely why Microsoft allows users to register multiple security verification methods. Additionally, Microsoft offers a 25-character recovery code that should be stored in a safe place. This code can help you regain access to your account if you lose access to your usual verification methods. Have you saved this recovery code? If so, have you tried using it to recover access to your account?
Please share the results and any exact error messages you receive, without including passwords, verification codes, or other sensitive information. This will help me determine the most appropriate next steps.