Here is how to convert UTF-8 numbers to UCS-2 numbers in hex:

<?php
 
function utf8toucs2($str)
{
       for ($i=0;$i<strlen($str);$i+=2)
       {
                $substring1 = $str[$i].$str[$i+1];  
                $substring2 = $str[$i+2].$str[$i+3]; 
               
                if (hexdec($substring1) < 127)
                        $results = "00".$str[$i].$str[$i+1];
                else
                {
                        $results = dechex((hexdec($substring1)-192)*64 + (hexdec($substring2)-128));
                        if ($results < 1000) $results = "0".$results; 
                        $i+=2;
                }
                $ucs2 .= $results;
        }
        return $ucs2;
}
 
echo strtoupper(utf8toucs2("D985D8B1D8AD"))."\n";
echo strtoupper(utf8toucs2("456725"))."\n";
 
?>

Input:
D985D8B1D8AD
Output:
06450631062D

Input:
456725
Output:
004500670025