Sundials works well because it stops all creatures. Phase Shields would only be an option is your opponent has creatures that do not have momentum. Otherwise, they still get through and hurt you.
Also, if your Sundial gets stolen (which never really happens, iirc) the stall is still in play. But if your Phase Shield is stolen, then you lose the protection all together.
(btw, I, too, want to add my thanks for sharing this deck. I thought that I would do some FG farming again, noticed this deck, and was surprised at how well it works.)