When you open a data discovery or presentation, it will open in landscape by default. To change the orientation to portrait, click the phone icon (green highlight below).
Presentations opened on your phone often display miniature visuals. Tap on a visual to view it in full-screen.
If the visualization has a legend, it will be denoted by a legend icon (red arrow above). Click the icon to open the legend.
Any slicers will be denoted by a slicer icon (blue arrow). Click the icon to open the slicer.
To interact with a data discovery, long-tap on the relevant data point to the context menu.
To interact with a presentation visual, first tap on the visualization to select it, then long-click to open the interaction menu.