Only thing to do there in my opinion (other than going to a beach) is to take the water taxi over to Atlantis. Truly a beautiful place. Unfortunately, they now charge $40.00 for their tour and severely limit access if you don't pay up.
First time on the island and loved it! Took a tour of the entire island (both Dutch and French sides, $25.00 p.p.) by taxi van. Driver had a PA system and gave us a very interesting tour. He dropped us back in Phillipsburg and we spent the afternoon wandering around. There is a very nice beach directly in front of downtown Phillipsburg too. We walked back to the ship but you can take the water taxi for $4 one-way or $7 r.t. Maho (aka Airport) beach is well-known for the planes that land directly overhead. We stopped there briefly on our tour but didn't see any large planes land. Great beach bar and a good place for a cold beer or to people-watch while waiting for a plane to land.