A number of years ago we stayed at this place a couple of times:
http://www.adirondackinn.com/
Great site, cottages, decks, gazeebos, bbqs, pool, etc.
Walking distance to the show too.
They used to have minimum night stays, but I just quickly checked online and it seems you can pull off a one nighter at the time of the Phish show.
Cheers,