Concourse is a fully responsive platform so there is no need for an Android nor iOS specific app to utilize the system on a phone or tablet. Concourse will automatically recognize the size of the device you are using and adjust the presentation accordingly.
That said, there are features of Concourse that will be more of a challenge to work with efficiently using a small screen. These largely cover the administrative interfaces. Editing can be done though we would not suggest an instructor type out their entire syllabus on a phone.