Tried a couple of different ways to do this but this seems to work best:
<?php
$info = ldap_first_entry($ds,$sr);
// get it binary-safe.
$bin_guid = ldap_get_values_len($ds,$info,"objectguid");
// convert to hex, bin2hex failed here for me. Unpack() seems to work though.
$hex_guid = unpack("H*hex", $bin_guid[0]);
?>