It might be easier to parse it in Javascript (perhaps using jQuery), and then send it to your PHP with some AJAX.
// Javascript/jQuery
var array = [];
$("h3").each(function() {
array.push($(this).html());
});
var message = JSON.stringify(array);
$.post('test.php', {data: message}, function(data) {
document.write(data); // "success"
}
Then in PHP:
<?php
$data = $_POST['data'];
// convert json into array
$array = json_decode($data);
// do stuff with your data
// then send back whatever you need
echo "success";
?>