Hi Kayla
It is possible currently to turn a Story Map Tour into a native mobile app that your readers can access via the various App stores. The app you create can feature one or more Map Tours. The product to do that is AppStudio for ArcGIS. The app you create is not a generic viewer: it is only used to view the Map Tour(s) that you build into it. No coding is required and the process of submitting the app to the App stories is done for you by AppStudio.
Apart from that, we don't have a mobile app currently. The Story Map apps are web apps that run in the web browser. The layout of the app changes to adjust to smaller displays like phones but it still runs in the web browser. We are considering some potential future development to utilize native apps, either for viewing or authoring, or both. Let us know if you have any requirements or thoughts about this.
Rupert
