Hi Dylan Murphy,
If you're having trouble accessing an older Xbox/Microsoft account, the best next step is to try Microsoft's account recovery options. Since the account was previously associated with your father's phone number but that security method is no longer appearing, the account's security information may have changed or may no longer be available for sign-in verification.
You can try the Account Recovery form and provide as much information as possible about the account that helps verify ownership. If you remember the email address associated with the account, start with the Microsoft account recovery process and follow the guided steps.
If the recovery form does not restore access, Microsoft Support may be able to provide additional guidance on available account recovery options. For security and privacy reasons, account access can only be restored after ownership is successfully verified.
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