On a phone, tap anywhere on the left or right half of the homepage tool card to turn back or forward, including the description under the picture. The tool's link still opens its page. On a computer, the shade that appears when you point at a side of the card is lighter, and the arrow shows without a circle behind it.
Homepage tool stack turns from anywhere on the card
On a phone, tapping either half of the homepage tool card turns the stack, not only the picture.