I think creating a new mysql user for phabricator would be the better way to go here and then grant all permissions on the phabricator database to that new mysql user.
In mysql prompt:
CREATE DATABASE database-name;
GRANT ALL PRIVILEGES ON database-name.* TO “user”@“hostname” IDENTIFIED BY “password”;
Where you can change ‘user’ to phab (or something else you like) and if you run mysql/mariadb on the same server (usualy the case on NethServer) hostname should be localhost, and where database-name is the name of the db. You can give that any name you want. It might be a good idea to name it phabricator.