Hmm.... The mystery deepens. I've just written to Phill about this. It's true that I did supply Phill with this species in sterile culture some years ago, but at that time it was so young as to make a positive ID when in the flask impossible. I did say at the time that I wasn't 100% sure of the ID. However, Phill is very field experienced and was subsequently happy it was OK. Of course, he may have also obtained cultures from elsewhere in the interim.
Nepenthes' apprearance vary a great deal depending upon the growing conditions they are under. It's hard to say from the posted photo exactly how large the plant is, but leaf texture, pitcher form and tendril length can vary. For example, N. ampullaria looks very similar to N. x hookeriana to start off with. However in this case, the leaf attachment seems wrong to me. From what I can see on the photo it is decurrent on the plant shown while that of N. argentii is somewhat petiolate, even when young.
Maybe we are all wrong and it is N. argentii. Whatever it is, I know that Phill would have shipped it in good faith, but mistakes can be made with small plants!