FWIW, it isn't just not meaningfully privacy-preserving: it offers essentially no privacy preservation at all. There are 10 billion possible US phone numbers, and we know from Bitcoin that you can search that space in something like ten seconds on a typical PC. You also only have to do this once to construct a lookup table that would only take a terabyte to store and index, and then you could offer anyone instantaneous reverse lookup from truncated hash to phone number. It is essentially meaningless "privacy theater".