The first manned landing on Phoebe was made by Martians eight years before the events of Leviathan Wakes, in order to be surveyed for ice mining (much like the rings of Saturn). When core samples from the moon were investigated, however, silicate samples were found, and the Martian government approached Protogen as a cosponsor of a long-term research facility.
After Protogen discovered the alien agent they dubbed the protomolecule (colloquially known as the "Phoebe bug" due to its origin) encased in Phoebe, they theorized that Phoebe was not a naturally formed planetesimal, but created as a weapon by extra-terrestrials 2.3 billion years in the past, and launched at a trajectory towards the Earth. It was, however, captured by Saturn's gravity, where it settled as a satellite.
The Labs Edit
The labs at Phoebe Station were a joint scientific venture between Martian and Protogen researchers. After the research team at Protogen had designed their planned tests for Eros, they trapped the Martian researchers in a lab and exposed them to the protomolecule to study its effects on humans. After the protomolecule killed the Martians, Protogen burned the bodies, purged the hard drives, and abandoned the station. All Protogen researchers were transported to Thoth station to make final preparations for the Eros experiment.
Eros Incident Edit
After the protomolecule was unleashed on Eros during the Eros incident, and its existence became known to the public, the Martian fleet bombarded Phoebe with nuclear weapons, vaporizing it into a thin gas that was sucked into Saturn’s gravity.