Episode of new podcast showing up only on iPhone, but not within iTunes

The extension on the URL for your media file is.aac - it should be .m4a (it's the same thing, but the latter extension is required for iTunes). Just change the filename to the different extension and the feed to match. When I checked the file in a browser it forced a download - this may have been because of the extension, but when you've changed the extension you should make sure it's not doing this - enter the new URL in a browser and make sure it plays directly in the browser, not downloads.

Your server is acting up, and giving different responses to different clients.

Subscribing in iTunes shows the presence of the feed but with no episode (it's probably actually seeing an error message as below).

Checking it in FeedValidator gets the message 'Server returned [Errno 1] _ssl.c:510: error:14077438:SSL routines:SSL23_GET_SERVER_HELLO:tlsv1 alert internal error '

Checking it in XMLGrid.net gets the rather clearer message 'The plain HTTP request was sent to HTTPS port'

Checking it using curl in Terminal shows the feed without problems.

The coding of the feed itself appears to be OK.

So you have a server problem, possibly related to the certificate for the https secure connection, and you need to take it up with the people running your server.

Incidentally the iTunes Store is showing the episode because it caches the feeds, and so it's showing it as of the last time it was able to read it: possibly indicating that the feed was previously OK - unless the server is reacting differently to the Store and the iTunes application, which is quite possible.

I'm glad to hear you've got it sorted.