I'm assuming that one or more flights on the day you originally booked got cancelled. At this point, US scrambles. Their preference is something simple, like just moving you to the same flight on another day.
You start by saying, "Gee I just noticed that ... Unfortunately, that's not going to work for me."
At that point, you can go whichever way you want, as in "Aren't there any alternative flights or routings that day?" or if you know of something in particular, you can suggest that. I don't know which day you were flying, and whether you were going back through PHL or through CLT, but you might want to check to see if the other flight is available on your day.