It's truncated hashes, not full hashes. So you don't see exactly which phone number it is, you get a bucket and the client checks if the full hash is in the buc

It's truncated hashes, not full hashes. So you don't see exactly which phone number it is, you get a bucket and the client checks if the full hash is in the bucket. Which is far from perfect, but it's a little better than the full hash.