Flex items grow to fit their nowrap text by default: the phone strip's cards needed min-width: 0

flex: 0 0 72cqw was enough to make each card in the phone strip 72% of the component's width.

the cards came out wider. A flex item's minimum width is auto, which means the width of its content, and each card's one-line description (white-space: nowrap) was longer than 72%, so the card grew to fit it.

styles.css lines 624–626; the phone screenshots and card measurements in the build notes.