This seems like smoke and mirrors to me:

  Traditionally, in Signal that process has looked like:
  
    The client calculates the truncated SHA256 hash of each phone number in the device’s address book.
    The client transmits those truncated hashes to the service.
    The service does a lookup from a set of hashed registered users.
    The service returns the intersection of registered users.

The phone number space is really not this big.