In case your environment uses ISA , the url that is shown may not reflect the actual port that your web application is using.
[What you have]:
ISA, SharePoint Web Server. ISA resolves the url for the web application on the SharePoint.
Here is the example:
The web application url without any visible port (hence we are assuming that it's 80:
To find out: Where is the web.config for the SharePoint web application ? Under what port the application is running?
[What you want to do]:
You can identify the port : Central Administration > Application Management > Web Application List