Sounds like a okayish loan at the least. He could be the Origi of the defenders, and kick on with us from now and earn a place in the squad.
He might go back to Stuttgart according to the Echo:
"Meanwhile, having seen Phillips make 11 appearances in all competitions during his time with Stuttgart, the German side have announced that the two clubs have agreed into looking into the possibility of the defender returning to Germany at the end of their winter break at the end of January."
IF that is the case, it'd suggest that one of Lovren or Matip could be back quite soon.
Either way really, all good! Having Phillips available through at least part of this busy spell is a positive.