See this suggestion that already covers it.
Currently, the mobile editor is designed to for reviewing and tweaking projects, with any serious development work intended to be done in the desktop version. Therefore not all features of the desktop version are available in the mobile version. In particular many features are difficult to add to the mobile version either due to the input method (e.g. drag-and-drop tends not to work on mobile, because it conflicts with pan scrolling, therefore requiring the feature is seperately re-implemented a different way) or due to the screen size (e.g. it's difficult to envisage how the timeline bar could even fit on-screen at the same time as the layout view on a mobile phone while still being useful, so it's not currently supported). All of this is solvable, but it takes extra work, and we're a small company with limited resources, dealing with thousands of bug reports, hundreds of other feature requests, etc.
You can plug in a keyboard and mouse to most mobile devices and then use it like a laptop. You can force C3 in to desktop mode in Settings, and then use the full feature set on something like a tablet with a keyboard + mouse.