Here is a dedicated thread to follow issues regarding mobile compatibility with OnlyOffice based applications.
A few GitHub issues that were open:
Basically those apps are super difficult to use on touch screens, and even more on small screen devices. Ideally we'd want them to be as easy to work on than on desktop.
Please don't hesitate to share here your experience with those apps on mobile.
In my opinion it'd be great if spreadsheets would start up with maximised space for columns & text, while the toolboxes are stripped away.