Are Views responsive on mobile devices?

Yes! Both Table View and DataTables layouts are responsive on mobile devices:

A Table View layout like this:

...will shrink to a vertical layout, so it looks better on mobile devices:

You can use this filter to disable this responsive mode:

add_filter( 'gravityview/template/table/use-legacy-style', '__return_true' );

Read here how to add this code snippet to your website: Where to put code samples.

DataTables, on the other hand, has a special mode called "Responsive Tables", which you can read more about here: How to Enable the Responsive Tables mode.