How to configure a PHP installation with the LDAP extension in Linux
I've never used cPanel (much less with WHM VPS) so I don't know where the knobs are. But there should be a place where you can configure PHP modules. There will probably be a list of available modules that you can enable/disable.
If the LDAP module is not in the list, you should get in touch with your hosting support to see if they can fix it or you are in charge of doing it (it depends on your hosting contract).