Another thought, did your plant come with a label with the grower's name on it? If it did, it's worth looking up their website and seeing if they have a catalogue of their varieties. Some commercial growers have list, and I've been able to get the trade-name of a couple Phals that way. In one case a quick google of the trade name actually turned up the proper RHS registered name. (Yes, commercial growers can give trade names to registered cultivars...
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) It's a very long shot, but worth checking.