Mobile-first design means creating apps and websites that work great on phones...

https://www.bookmark-suggest.win/mobile-first-design-means-building-apps-or-websites-starting-with-smartphones

Mobile-first design means creating apps and websites that work great on phones first. It’s faster to load, with big buttons and easy-to-tap features that fit your screen. The menus are simple, so you can find what you need without fuss