Custom amplify passwordless auth for flutter

Been following up on the following post. https://aws.amazon.com/blogs/mobile/how-to-create-a-one-time-password-authentication-flow-using-amplify-flutter/

What I am trying to achieve is auth using just the phone number, no password or email.

Article points me in the right direction, but wanted to know if there was already another resource for phone number & SMS otp? If not, two more questions please;

1. I'm assuming what I need to look at is replacing SES with SNS, is that correct?
2. Is there a reason, maybe security related, that email otp is supported, while phone number is not?