There is no multi-socket Phi - I asked about it at an Intel booth at a conference a while back and was told the delta between memory bandwidth and inter-socket bandwidth would be so great that it would not be a useful configuration.
I believe the talk of NUMA refers to the single socket behaving like a cluster with up to 4 NUMA domains, but I can't find any good references right now.
Ah, interesting; I hadn't read that anywhere. From the limited reading I just did, it does seem like that's a configuration they offer, but from the scant sources available I can't quite figure out to what extent it's actually necessary to extract maximum performance out of the machine (compared to just artificially pinning each core to disjoint memory). Either way, good information--thanks!
I believe the talk of NUMA refers to the single socket behaving like a cluster with up to 4 NUMA domains, but I can't find any good references right now.