linking to a specific page to generate wordpress.

I am trying to include a page within a wordpress published page (https://brianschroeter.com/a123test/?page_id=11) the issue I am having is that the proxy.php page that i am including is suppose to funnel a feed of sorts so I need to tell the feed the page to load the file on. ex: https://brianschroeter.com/a123test/index.php or https://brianschroeter.com/a123test/page_11.php any ideas on where I would actually link to or how I can tell the direct page of ?page_id=11

Thanks anyone and everyone for your help in advance!
-Patrick