Kai Yang says CUBRID PDO driver doesn't support connection string parameters at this moment. When specified, it simply drops them.
Since PDO/PHP drivers are based on CCI, they should be able to support any CCI connection string parameters without a problem.
Please add these parameters support.
For a reference, see cci_connect_with_url() API for a list of available parameters. altHosts, loadBalance, rcTime and loginTimeout are among the most frequently important especially in HA and CUBRID SHARD environments.