Mobile-first design means building apps and websites with phones in mind first....

https://oliviasinsightfulthoughts.novacrestiq.com/posts/do-descriptive-labels-matter-on-mobile-or-is-placeholder-text-enough

Mobile-first design means building apps and websites with phones in mind first. It makes everything load fast, so you don’t waste time waiting. Buttons and menus are easy to tap with your fingers, and navigation is clear and simple