3/5 for the duration, and 5/5 will get weaker as levels go up. At 75 3/5 was better then a Phalanx cast from PLD's native skill, now it's not. There most definitely is a difference between the two at 5/5

Phalanx 1
((Enhancing magic skill - 300) / 29) + 28

Phalanx II
((Enhancing Skill/25) + (3 * Merit) +1)

Each increase in merits increase's the effect by 3, so going fro 3/5 to 5/5 only adds 6 more base, making it 4~5 or so stronger then PLD's. And this was me with 420+ skill vs a PLD who cast in capped skill but no gear swaps. Basically it's not worth wasting 3 tier II merits in, 5 would be downright crazy seeing as you have to give up on something else and can get the EXACT same effect (@90) by going /SCH.

Now if SE would change it to a scroll and give is "enhances phalanx effect", merits, then I might be interested.