Esri Story Maps team member and cartographer Cooper Thomas writes:
All of the Story Map apps are optimized for mobile devices and feature responsive layouts. Occasionally, however, you may wish to present a slightly different version of your story to readers using small devices. Perhaps the “main,” desktop-oriented version of your story uses 3D scenes, which aren’t supported by most tablets and smartphones; perhaps you’d like to use portrait-orientation images to maximize screen real estate; or perhaps you’d simply like to abridge your story to cater to on-the-go readers.
Read the blog post on the Story Maps Developers' Corner blog: