The Problem
The main problem with using filters on mobile devices, particular on smartphones, is placement of a widget with filters. If you place it above the products grid, it will take up too much space and move the grid down. If you place it under the products, then it will be inconvenient to scroll page to the filter widget every time.
In this case, it is optimal to place not the filter widget above the products grid, but the button that opens it only when needed.
Depending on version (Free or PRO) of the Filter Everything plugin, you have different ways for solving this problem. You can either open filters list above products by clicking on the Filters button or the Filter widget will appear as a pop-up when you need it. The second solution is more universal and is present only in the PRO version.
Pop-up Filter widget
To enable the Filters pop-up widget, you need to go to Filters > Settings and activate the “Use Pop-up Filter widget” option and save settings. After that, the Filters button should appear above the products list and be visible on smartphones only. A click on the button will open Pop-up Filters widget.

If you have problems with this button, please read this article.
Collapsible Filter Widget
To configure unfolding of the Filter widget, you need to enable the “Collapse Filters Widget on Mobile devices” option in Filters > Settings. After that, the Filters button should appear in the place where the Filters widget is displayed, and be visible on smartphones only.
If the sidebar with Filters is displayed under the products list, try enabling the “Sidebar on top” option in Filters > Settings. If that doesn’t help, please ask your site’s webmaster to help you.
In Addition
Both of options assumes that the Filters widget is present in the sidebar, which is displayed on smartphones. If it’s not there yet, please add it on Appearance > Widgets
Important: if several Filter Sets are used on the page, the widget with highest priority will be opened by default.
Both versions of the Filters widget on Mobile devices are compatible with the AJAX feature and become more convenient to use if it is enabled.
If you enable both options at the same time, the pop-up widget will be displayed as a higher priority.