PHP/LDAP Setup Problem

I need to add LDAP support to my install of PHP. I had my sysadmin download OpenLDAP and install the libraries. Our current build of PHP is complex and I'd prefer not to have to rebuild just to add LDAP. I've been told to use the dl() function to load the LDAP library when needed in PHP. Whenever I dl("libldap.so") PHP returns the following error: PHP Warning: dl(): Invalid library (maybe not a PHP library) 'libldap.so' in ..... What am I doing wrong? Thanks in advance. Jim