$wp_hasher = new PasswordHash(8, TRUE);

$password_hashed = '$P$B55D6LjfHDkINU5wF.v2BuuzO0/XPk/';
$plain_password = 'test';

if($wp_hasher->CheckPassword($plain_password, $password_hashed)) {
echo "YES, Matched";
} else {
echo "No, Wrong Password";
}
?>