Find the inverted value of the string
The title of the question is confusing. The code seem to check if the text is not the same if you read it backward. For example, it $b will be true for "hello" and false for "level". In other words, you're checking if some text is NOT a palindrome. I think you should change the title to better reflect what the code is doing.

Things to improve:


It's enough to iterate until strlen($text) / 2, no need to go all the way until the end
To avoid re-calculating the length of the string, it's better to calculate it once before the loop and reuse it
Wrap the whole thing in a function to make it easier to reuse and to test
The !== is unnecessary, a simple != would do


For example:

function isPalindrome($text) {
    $length = strlen($text);
    for ($i = 0; $i &lt; $length / 2; $i++) {
        if ($text[$i] != $text[$length - 1 - $i]) {
            return false;
        }
    }
    return true;
}

function test_isPalindrome($text) {
    printf("isPalindrome(%s) -&gt; %s\n", $text, isPalindrome($text) ? 'YES' : 'NO');
}

test_isPalindrome("reverseesrever");
test_isPalindrome("hello");
test_isPalindrome("aba");
test_isPalindrome("aa");
test_isPalindrome("ab");


Outputs:

isPalindrome(reverseesrever) -&gt; YES
isPalindrome(hello) -&gt; NO
isPalindrome(aba) -&gt; YES
isPalindrome(aa) -&gt; YES
isPalindrome(ab) -&gt; NO