I know it's fantasy but which sub-category would it be in?
I don't know about the specific fantasy sub-genre - probably Young Adult - but every book of the Harry Potter series is a different one of the classic seven genres.
1 - Puzzle (there's a series of challenges - even before the end - they have to figure out . . . it's not a mystery: The whole book, they think they know who the bad guy is, they aren't trying to figure it out.)
2 - Mystery (they're looking for the killer in an ongoing series...)
3 - Horror (crazed escaped killer with a knife, werewolf, dementors...)
4 - Quest/Challenge - (Triwizard Cup, and even the ending, are dangerous episodes our hero faces alone and has to survive.)
5 - Tragedy (Harry has a weakness for heroism, someone dies for it - but there's also a long list of people who's faults were pointed out to have caused the end, including Dumbledore's and the victim's)
6 - Comedy (there's humor, romance, you see the bad guy crying, the reader already knows much about what's going on, the hero is portrayed as crazy even when he's right, even the big-bad-thing-at-the-end ..... well, spoilers)
7 - Action
So . . . take your pick.