Viewing ACIM Web Edition on your phone (is there an app?)

While, there is no native app for the ACIM Web Edition on desktops, phones, or pads, you can use it on all of these devices (Windows, Mac OS, iOS, Linux, etc.) by just opening your web browser and going to https://acim.org/acim/en.

You can bookmark that page for quick access in the future.  And if you're using it on a mobile phone, you can also add a shortcut to your phone's home screen using the instructions here.