The shield part is... why would anyone use this card instead of another copy of your shield?
D'oh, that's actually a really good question. I haven't thought of it like that.
However, I guess using its secondary effect and deck thinning has its benefits over some dead draws, so...
I mean, it's the same. Instead of having N shields I will have N-M shields and M Phalanx. If you draw the Phalanx, you still have to pay the shield you draw with it.
A possible change would be playing the shield automatically, and still has to be a little bit cheaper immo. This way people can play a shield cheaper if they draw Phalanx.
Yeah, if the effect was only drawing a shield. However, you forgot that the effect also doubles the HP of all creatures and thins the deck by drawing a card. Stop thinking about the shield effect as a primary effect and instead think of it as a bonus for doubling everything's HP.
Also, in the case where you would want to draw two specific shields. For example, if you want a Permafrost and an Emerald, and are playing a rainbow or something, then it may be more wise to run 1 Permafrost, 1 Emerald, and 2 Phalanx instead of 2 Permafrost and 2 Emerald.
Needless to say, I'll drop the cost to 3/2 anyways.