Create while loop for feed

So I am pulling in and parsing an rss feed with this script:

<?php
error_reporting(E_ALL);

$xml = file_get_contents('http://feedurlhere');

// MUNG THE XML BECAUSE WE DO NOT HAVE THE NAMESPACE INFORMATION
$xml = str_replace('content:encoded', 'content__encoded', $xml);
$xml = str_replace('isc:',            'isc__',            $xml);

// CONVERT THE XML TO AN OBJECT
$obj = SimpleXML_Load_String($xml, 'SimpleXMLElement', LIBXML_NOCDATA);


// GET SOME FIELDS
$item_title = $obj->channel->item->title;
$item_link = $obj->channel->item->link;
$item_description = $obj->channel->item->description;

echo "$item_image<br/><strong>$item_title</strong> $item_description<br/>";

?>


My question is... Currently this script just returns the variables from the latest entry in the feed. How do I create something like a while loop that returns everything in the feed?