[curt.clifton]

I'm afraid it's not really a matter of the computer "broadcasting", it's a matter of the routers between your computer and the rest of the internet blocking the requests coming from your iPhone. Changing settings on your computer won't affect that.

Unless you can configure the routers, or whoever configured them was somewhat lax about security, it is unlikely that your iPhone will be able to connect to your computer. (I don't mean to imply that the OmniFocus web interface is insecure. It's just that routers are often configured to block all traffic that is not explicitly allowed.)