Well lets compare it to the spider which is a 4/2 for 3. If you were to increase the cost to 3, the spider is going to be preferred in most situations since you aren't hurting yourself, however it would still have its uses because it ignores shields. The upgraded version however is 7/2 for 4 versus 5/1 momentum for 2. This is a no contest for fractal rushing since you can play two phages for every one spider.
So, a nerf is in order. A cost increase would out it on par, and would still be useful for rushing, but another option would be to increase the damage done to self. I'd prefer the damage increase since it is part of the uniqueness of the card and it requires some more thought in deck making. If you go purely offensive you leave yourself week against another rush deck, and if you bring healing or protection you slow your deck down leaving it weaker to slower decks.