I considered the Shelter, which is a very nice cartridge and should have more than enough output to work well with the Lamm. However, I preferred the EMT JSD5, as it had much of the midrange of my Koetsu RSP, better bass and dynamics, and a good deal of gain (I only use the step up because it was ideally matched for the cartridge and a better loading match than the transformer in the Lamm's MC stage, not for the additional gain). Works well with my Graham 2.2, also, so it should work nicely with your Phantom. The Shelter sounded a little less vivid and lush to me (I almost want to say a little homogenized in comparison, but that would not be fair to the Shelter, which really is one of the better ones out there), and I wanted those qualities because I listen primarily to classical music and admit that I like the Koetsu "sound". A lot of the modern cartridges are sounding more and more like CD to me, which is what a lot of people like; I prefer a little more of the old-fashioned vinyl warmth.
By the way, very nice system!
By the way, very nice system!