I think your parent comment is saying MS flags the account as questionable and asks you to confirm your current phone number (the one you already used a burner for).
Having TOTP enabled should ward off the "suspicious login" prompts that ask for your phone number. If they still want your phone number for whatever reason, you'll have no choice but to buy another burner phone, but there's no reason they wouldn't accept a new phone number. You did remove that phone number from your account, after all (people change their phone numbers all the time).