You can use arrays for multiple attributes example:

<?php
$entry[mail] = array("example@example.com","example2@example.com");
$results = ldap_mod_add($ldapConnID,$dn, $entry);
?>
or as i did for creating anew user:
<?php
$adduserAD["objectClass"] = array("top","person","organizationalPerson","user");
?>