Usually, under settings, (if you really dont know) (!!!, wry), usually under settings it asks you for an email address, and an Aus mobile phone number, the more modern systems now can use the sensor on the phone to sense your finger print, or your face.
Telstra will ask for first, to send a code to your main mobile phone #, even if that phone number is not with Telstra, and then as a 2nd back up, will also send a code to your email address.
Google, will send a question "is this you" to a linked device, you click yes, and it lets you in.
Usually, when you first set up a device, or app, it will ask for a mobile phone # and an email address.
Scammers who are cunning will firstly change the mobile phone #, and then change the email address, then they can get 2fa sent to their "new" numbers.
Porting is now too easy, as in phone numbers.
===---===
Ubuntu, what a name, keep getting a lot of that for an email address I look after for an old man, ...
Or something called "wijl.*n*o".
---
Also, yahoo will allow a block sender limit of 1000, not good if an old man wont listen, and not go on a website looksee, and add his email address to all and sundry.