Actually, you probably do have to go to the 800- number to get a definitive answer.
But, here are my guesses: 1) You have to spend at least 2 cents in points (20 points) plus spend at least $15. 2) Sometimes there are "offer details" you can find a link for -- in tiny notation on the offer itself. The details may indicate that you have to spend ALL of your points, or $15 worth of points to get the offer. But, if it just says, spend points, you would have to spend at least a penny or two of points. 3) Maybe it means that you have to spend as many points as you will get back in the offer.