According to the search results, Amtrak offers train routes across the United States, including the Northeast and Midwest regions. However, none of the search results provide a direct answer to the question of which Amtrak route services Philadelphia to Chicago. To find the answer, we can go to the Amtrak website and use the "Find a Train" feature.

Using this feature, we can see that the Amtrak route that services Philadelphia to Chicago is the "Pennsylvanian" train, which runs daily between New York City and Pittsburgh, with stops in Philadelphia and other cities along the way.

Therefore, the Amtrak route that services Philadelphia to Chicago is the Pennsylvanian train.

References: https://www.amtrak.com/train-routes https://www.amtrak.com/trains-to-chicago https://www.amtrak.com/northeast-train-routes https://www.amtrak.com/home https://www.amtrak.com/midwest-train-routes https://www.amtrak.com/train-schedules-timetables https://www.amtrak.com/pennsylvanian-train