By default, when you are connected on a call, the phone shows details of that call and soft key actions you can perform for that call. In order to see details of a waiting call, you need to scroll the display using the up and down cursor buttons.
You can opt to have the phone automatically show details of a waiting call when one alerts the phone and soft key actions that you can perform on the waiting call. If you use the scroll keys to return the display focus to the currently connected call, the focus automatically returns to the waiting call after a few seconds.
To do this during a call, press the PHONE key and then press Features.