Currently our forms are fixed width. This is something we hope to provide in the future but I can't say when.
I agree this would be extremely useful. Currently the option is to export form to PDF fillable, then download a reader on your phone and use that to fill it out. Even if we could purchase an option to create a mobile application or a mobile form it would be extremely beneficial.
The PDF is also fixed width. Mobile users can fill out web forms (no app needed) - they just don't reflow.