Phantom Dancer allows you to ignore unit collision when you have it, but if you were to sell it, you will still ignore unit collision.
Steps to reproduce
1. Buy a Phantom Dancer.
2. Make sure that the Phantom Dancer is allowing you to ignore unit collision
3. Sell Phantom Dancer.
4. You will still ignore unit collision.
© 2013 Riot Games, Inc. All rights reserved. Riot Games, League of Legends and PvP.net are trademarks, services marks, or registered trademarks of Riot Games, Inc.