<?php

$str = 'uvjWEHTUk1LnzVZul9ynRpezWfKYN3bvlx103wxACxo';
$bin = base64_decode($str);

if (strlen($bin) % 8 !== 0) {
	throw new \RuntimeException('data length should be divisible by 8');
}

$result = '';

for ($i = 0; $i < strlen($bin); $i += 8) {
	for ($j = $i + 7; $j >= $i; --$j) {
		$result .= bin2hex($bin[$j]);
	}
}

echo $result;