sha256 crypt password hashing




I have setup a Postfix/Dovecot/Roundcube Debian server for one of my clients

With Dovecot I can generate a password hash using the following command:
doveadm pw -u usernameATdomain_com

I have set the security level with the following parameter :
default_pass_scheme = SHA256-CRYPT
with this scheme I obtain $5$ prefixed hashes that
are 63 characters long (prefix included)

I'd like to allow my client to manage his own users i.e.
create virtual users and set their passwords via phpmyadmin
Unfortunately phpmyadmin doesn't come with a hash calculator

I knew a website that could generate such hashes but it no longer exists.

There are a multitude of other online calculators/generators
that provide sha-256 hashing (64 characters) but none provide hashes
containing the $5$ prefix

Could this be the distinction between sha256 vs sha256_crypt ?
Or am I after a red herring ? I'm a little confused with this prefix issue

This is what is stated on Dovecot's Wiki Password Schemes page:
SHA256-CRYPT: A strong scheme. The encrypted password will start with $5$

My current solution is to have the client create a virtual user with a blank password and then to use the password plugin present in Roundcube to register the desired password.
any better ideas ?