Actually, I'm an eliminativist about phenomenal states. I wouldn't be completely surprised to learn that the illusion of phenomenal states is restricted to humans, but I don't think that this illusion is necessary for one to be a moral patient. Suppose we encountered an alien species whose computational substrate and architecture was so exotic that we couldn't rightly call anything it experienced 'pain'. Nonetheless it might experience something suitably pain-like, in its coarse-grained functional roles, that we would be monsters to start torturing members of this species willy-nilly.

My views about non-human animals are similar. I suspect their psychological states are so exotic that we would never recognize them as pain, joy, sorrow, surprise, etc. (I'd guess this is more true for the positive states than the negative ones?) if we merely glimpsed their inner lives directly. But the similarity is nonetheless sufficient for our taking their alien mental lives seriously, at least in some cases.

So, I suspect that phenomenal pain as we know it is strongly tied to the evolution of abstract thought, complex self-models, and complex models of other minds. But I'm open to non-humans having experiences that aren't technically pain but that are pain-like enough to count for moral purposes.