what is the ideal layout screen size for phones?
min width of 320px and max width of 499px
375px minimum - no phone is smaller than that.
I’d recommend using Chrome’s dev tools
- Right click → Inspect
- Device toolbar (Ctrl + shift + M)
- Select the preferred device / viewport
Admittedly it’s a small share of the market but the newer fold phones have narrower outer screens, so someone could conceivably browse on a ~340px screen.
Although that’s probably not an edge case worth worrying about.