If you want to disable/enable chase referral option, you need to first set the protocol version to version 3, otherwise the LDAP_OPT_REFERRALS option will not have any effect. This is especially true for querying MS Active Directory.
<?php
ldap_set_option($ds, LDAP_OPT_PROTOCOL_VERSION, 3);
ldap_set_option($ds, LDAP_OPT_REFERRALS, 0);
?>
And as always, these should be called after connect but before binding.