Mobile-first design means building your website or app starting with phones in...

https://www.newpelican.com/articles/why-mobile-first-design-has-become-the-standard-for-modern-digital-services/

Mobile-first design means building your website or app starting with phones in mind. It’s all about speed, so pages load fast on smaller screens. Buttons and menus are easy to tap with your fingers, making everything feel natural