Of course.
What “main” account? root (or the system admin)? They do. But, the domain you’re installing phpPgAdmin into does not. They can only manage databases in their domain.
So, create a database in that domain.
If you want that domain owner to be able to manage existing databases, you’ll need to grant their database user access to them. It’s possible to manage any database on the system with phpPgAdmin, once installed, assuming they have access to them.
I’ll also point out there is a PostgreSQL management GUI in Webmin, which the root user (and any domain owner, assuming you grant them access) can use without having to install any extra software.