The clearinghouse may not have the user’s most recent email address, which is common amongst non-tech people. My mom and aunts have lost many email addresses this way and forcing them to use an older email would cause many issues.
>>supriy+(OP)
The app has to ask for email/phone to begin with (see step 1), if the email doesn't match then phone would be used as fallback, or potentially as a "Didn't Receive Code?" gesture.