Solution :

uksort($locationArray, function ($key1, $key2) {
    // Extract letters from keys
    $letter1 = substr($key1, -1);
    $letter2 = substr($key2, -1);
    // Compare letters
    $letterComparison = strcmp($letter1, $letter2);
    // If letters are the same, sort by numeric part of keys
    if ($letterComparison === 0) {
        $numericPart1 = (int) substr($key1, 3, -1); // Extract numeric part of key1
        $numericPart2 = (int) substr($key2, 3, -1); // Extract numeric part of key2
        return $numericPart1 - $numericPart2; // Compare numeric parts
    }
    return $letterComparison;
});

Solution :

uksort($testArray, function ($key1, $key2) {
    // Extract letters from keys
    $letter1 = substr($key1, -1);
    $letter2 = substr($key2, -1);
    // Compare letters
    $letterComparison = strcmp($letter1, $letter2);
    // If letters are the same, sort by numeric part of keys
    if ($letterComparison === 0) {
        $numericPart1 = (int) substr($key1, 3, -1); // Extract numeric part of key1
        $numericPart2 = (int) substr($key2, 3, -1); // Extract numeric part of key2
        return $numericPart1 - $numericPart2; // Compare numeric parts
    }
    return $letterComparison;
});