Hey there! Nice to meet you!
If you can access your Microsoft account, you may update your security info on account.microsoft.com > click "Security" > "Other Ways to Sign in" > "Use your password" > From here, you will need to add your updated verification method first on "Add another way to Sign in to your account" > Once you have successfully added your updated security info, you may remove your outdated recovery phone number.
Please be advised that adding a phone number as security information has been phased out, as stated in this article, particularly under "Note" https://support.microsoft.com/accounts-billing/manage/microsoft-account-security-info-verification-codes
Thank you for your understanding.
Best regards,
Darhyl