<?php
$feed = 'https://feedburner.google.com/
api/awareness/1.0/GetFeedData?uri=ИмяФида';
$ch = curl_init();
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_URL, $feed);
$feed = curl_exec($ch);
curl_close($ch);
$xml = new SimpleXMLElement($feed);
$fb = $xml->feed->entry['circulation'];
echo $fb;
?>

результат в сайдбаре