How do you design a store for one-handed phone use?

Put what people tap most within reach of a thumb, at the bottom of the screen. Search, cart and the buy button belong in the lower half, not in a top corner.

What decides it

Then check on a real phone rather than a resized browser window. Tap targets that are comfortable with a mouse are frequently too small and too close together for a thumb in motion.

The part that gets skipped

Most design decisions on a store are really navigation decisions, and navigation is what decides whether somebody finds the thing they came for.

A product page has one job. Everything on it that is not helping somebody decide is in the way.

Consistency beats cleverness. A customer learns your store once, and every screen that behaves differently costs them.

Where an app fits

The same screen designed several ways is the point: a catalogue of four hundred lines needs a different home screen from one of forty.