Malignant robots/nanites left over from the Martian civil war which attack the Oubliette and destroy the terraforming efforts. They are self-replicating and dangerous. Citizens in the Oubliette who are in The Quiet are often tasked with keeping the Oubliette secure from the ravages of the Phoboi, including managing the vast musculature that keeps the Oubliette moving and protected from the Phoboi.