Mobile-first design means creating apps and sites that work great on your phone...

https://foxtrot-wiki.win/index.php/Is_It_Better_to_Cut_Features_on_Mobile_or_Keep_the_Same_Experience%3F

Mobile-first design means creating apps and sites that work great on your phone right from the start. It focuses on fast loading, easy-to-tap buttons, and simple menus you can use on the go