There may be cases where we drop low traffic sites from our index, which is separate from the search index. I don't how much of that is public information, so can't go into detail.
Well but my point is why can't Google recognize these phone-number-lookup sites as the chaff that they are? Nothing should rank lower than them in any search that would return their pages. Said another way: it should be harder for them to clog the top of the SERPs (of course "them" could imply any number of topics).