In the resetting root user video, how did the new sys admin log into the root account if MFA was turned on and assigned to the phone of the previous one?

It looks like there are two options:

"Now, your root user can use the AWS sign-in page to verify your root account’s email address and phone number. Then, the root user can deactivate the lost MFA device and set up a new MFA device in its place. Note that this information verification feature is available only for AWS root users with a phone number associated with their root account. If your root user does not have a valid phone number associated with your root account, the root user must call AWS Support to reset the lost MFA device."

https://aws.amazon.com/blogs/security/reset-your-aws-root-accounts-lost-mfa-device-faster-by-using-the-aws-management-console/