The MD5 of PHP returns a result encoded in base16. But the LDAP MD5 returns a string encoded in base64. 
$pwd="toto";
$pwd_md5=base64_encode(mhash(MHASH_MD5,$pwd));
Just add "{MD5}" front $pwd_md5 to obtain the same format as LDAP directory.

Bye
Aur?lia