Another thing, I thought Phantom stock referred specifically to negative balances held at the DTCC (which led to other people having too high a balance).

Really the whole thing is a giant mess - people are settling trades - not by updating the company shareholder register but by increasing a balance at some counterparty - taking their word for it that they have shares either in their own name on the shareholder register or held with some other counterparty and that none of the shares are overcommited to other obligations. It's crazy. Central counterparty clearing was supposed to address this but it absolutely doesn't because the central counterparties don't actually hold the shares either - they use sub-custodians which are again the same big banks as before. So when your brokerage settles a trade through a central counterparty all that happens is that central counterparty updates it's accounts at citibank or hsbc or wherever.. but noone checks to see if citibank or hsbc really has those shares or that they aren't commiting them to multiple clients.