Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Sorry to hear you are having trouble recovering the account. The Microsoft username lookup page only displays a masked hint for security reasons; it does not provide the complete email address.
Since the account is already being used to sign in to the laptop, are you able to log into it using any other method or Windows user?
If the phone number was configured as a sign-in alias—not only as security information—you may also try entering the phone number directly on the Microsoft account sign-in page. Microsoft accounts can support an email address or phone number as the sign-in username.