PhF = "Phantom Flusher." Its monikered so because we don't know who it is, but someone is sending massive amounts of blocks through TA members' addresses, and even some DPC and SO/TI members are benefitting from this.
While we don't know who it is, we are nearly positive that it is a trojan, but it appears to be a "smart" trojan, as members' keyrates have tended to level off around 25k blocks per day each. Most trojans can be proved as such by an exponential increase in the keyrate of whoever's email address is in the client.