Hi Chris,
From what I can tell, the value from profile->outbound-proxy is passed into sofia NTATAG_DEFAULT_PROXY() and accepts a url_t structure [1], which clearly allows for a port to be specified [2]. However, I was unable to find any working examples from others on setting a port value inside outbound-proxy, nor did the documentation reference this.
Can you please tell us;
* Are you running against the latest stable version of FS?
* Have you tried this against the most recent master?
* Can you please pastebin the logs of what happens when you try including a port?
Once you've sent this through, we can determine if it's a bug or not.
Hope this helps
Cal