I don't think you are the only one that has run into this problem. I found out about the portal (https://my.physics.uiuc.edu/gradstat/login.asp
) after I let pop-ups display through my web browser when I was filling out my UIUC app. I got lucky. However, the form is essentially a ranking of your preference for working in different groups in the department. To me it does not seem to be all that essential. That is, nothing I didn't already say in my SOP, although the site does provide some information about the status of your application.