It was the 4 x 100 and splits don't tell the whole story.
Phelps did swim in both finals, and they won both, so wasn't sure which you meant.
But while we're on the subject, what exactly is 'the rest of the story' past the time you actually contribute, in a competition where the object is to put in the lowest collective time, and you're tasked with the exact same swim as your teammates (except the first leg). I'm not asking about this particular race, as I only watched the 200, not the 100.