Also, phasing isn't entirely un-hittable. It's just a much less accessible wavelength. Both Vision, J'onn, and others have been hit in intangible form by blasts of different frequencies.
Surfer has done this before with great success, and I would imagine that if Thor can deal with an intangible Vision, that it's reasonable to assume that BRB could do the same.
But keep in mind we said it'd be a good fight. And it would. I might even give J'onn a few victories occasionally (3/10-ish)