It's also vulnerable to the ubiquitous large laser and, ironically enough given its FWL flavor, the LGR; both weapons that wouldn't kill the Raiden or Grenadier you mention.
I agree with the point you raised about it being able to survive a Clan medium laser hit, something I consider a must have, but despite that the Phalanx is without a doubt lightly armored for its weight class. I wonder who infected who: the FWL's battle armor designers or their naval architects?
