function hexToStr($hex) {
    $string='';
    for ($i=0; $i < strlen($hex)-1; $i+=2)
    {
        $string .= chr(hexdec($hex[$i].$hex[$i+1]));
    }
    return $string;
}
function strToHex($string) {
    $hex='';
    for ($i=0; $i < strlen($string); $i++)
    {
        $hex .= dechex(ord($string[$i]));
    }
    return $hex;
}

$hex = strToHex('VOVA1234');
$str = hexToStr($hex);

echo "Hex: ".$hex;
echo "<br>";
echo "String: ".$str;