The Mobile view of each Layout defines how it will be displayed when viewed on a mobile device.
How to edit the Mobile view
Selecting the Mobile view
Select the desired Layout, then use the view selector to select Mobile :
When creating Widgets from another view (the Desktop view for example), the Mobile layout is generated automatically depending on available space and widget size.
Often, you may need to later tweak this automatic Mobile layout manually in order to create a good-looking Mobile experience.
When the selected view is the Mobile, then the Preview button shows a small pop-up window shaped like a mobile phone.