The password is not the instance ID but...
The documentation is wrong with this current ami I believe. The username and password is admin:password for the web front end. SSH I have not been able to go into yet because we only use SSM and the agent is not installed by default. Jury is still out on the rest but at this time it all looks the same as an OVA or a bare metal install.
password 'password' didn't work, SSH in and run sudo phenv python /opt/phantom/www/manage.py changepassword admin to set one (username is admin