If you're walking from the castle, then pass under the castle, ahead you will the carousel and to the left of the carousel is Philharmagic.
If you're walking from Liberty Square/Fronteirland, walk up the path past the Haunted Mansion, passing Peter Pan and It's a Small World. Philharmagic will be on your right. If you pass the carousel, you've gone too far.
If you're coming from tomorrowland, walk up past Ariel's Grotto and Pooh, walk around the carousel, bearing towards the castle and it's opposite the carousel.