To make a connection to a firebird database with pconnect many people like to use the SYSDBA, or database owner.
$dbConnection = ibase_pconnect('path to db','SYSDBA','masterkey');
The above is fine unless you want to login in various user that have different permissions. To use permission make roles in the database, either as the database creator (or SYSDBA) and grant the roles to the various users.
If you login with...
$dbConnection = ibase_pconnect('path to db', 'USERNAME', 'userpassword');
...interbase will default your user to the PUBLIC role, which is created when the database is create and usualy has select rights on tables only. To get the proper role you will need to use all the parameters, like this...
$dbConnection = ibase_pconnect('path to db', $user, $password, '', 0, 3, $role, 0);
BTW - The "path to db", is formed like this...
reading the interbase material, it states 3 connection methods, PHP appears to have selected the tcp type for us. So you can use localhost, or I suspect(never tested this myself) a ip address.