If your getting a error when saving your Magento configuration when using Phoenix varnish cache module: Fatal error: Call to a member function generateDesignExceptionSub() on a non-object in app/code/community/Phoenix/VarnishCache/Model/Observer.php on line 325

This should sort your issue out. Open up app/code/community/Phoenix/VarnishCache/Model/Observer.php and comment out the below function:

/**
 * Shows notice to update Varnish VCL file
 *
 * @param Varien_Event_Observer $observer
 * @return Phoenix_VarnishCache_Model_Observer
 */
public function showVclUpdateMessage(Varien_Event_Observer $observer)
{
    try {
        Mage::getSingleton('core/session')->addNotice(
            Mage::helper('varnishcache')->__(
                    'Update Varnish VCL with design exceptions by using the following snippet:'
            )
        );

        $designExceptionSubSnippet = Mage::getSingleton('varnishcacheenterprise/vcl')
            ->generateDesignExceptionSub();

        $designExceptionSubSnippet = str_replace(' ', ' ', $designExceptionSubSnippet);
        $designExceptionSubSnippet = nl2br($designExceptionSubSnippet);

        Mage::getSingleton('core/session')->addNotice($designExceptionSubSnippet);
    } catch (Exception $e) {
        $msg = 'Failed to prepare vcl: '.$e->getMessage();
        Mage::helper('varnishcache')->debug($msg);
        Mage::throwException($msg);
    }
}