During the initial phases of the expansion from Earth, Mars was earmarked as an agricultural food basket for the fledgling CSA. The terraforming project was hugely expensive, financed both by the Solar government and several corporate backers, and took over a century to change the desolate planet to a point that humans could survive outside of radiation-shielded domes. These days, Mars is the official capitol of Sol, boasting a population of six billion people living in the dome cities, and huge shipbuilding and administration facilities sailing above in orbit. The chief export is biomass; Mars is still one of the only planets in the solar system capable of supporting mass industrial farming.
Phobos is a shipbuilding and advanced naval system research and fabrication hub with mixed corporate and government presences. Significant portions of the moon's surface are dedicated to naval facilities, both for ship production and personnel training. During the settlement of Mars, Phobos was also the coordinating hub for colony activities, directing the terraforming project established on its sister moon, Deimos. The moon has a markedly poor reputation with Sol military personnel, who have often publicly stated that getting a posting there is like 'Hell on Earth' due to hostile conditions and demanding surprise military exercises.
Deimos was the muscle of the Martian terraforming project; the machinery used to alter the atmosphere and direct ice asteroids into strategic areas of the planet is still in operation today, but now serves primarily as a mechanism for regulating the planet's rather rambunctious weather systems. The rest of the moon is the property of the CSA and serves as the bureaucratic and administrative seat for Mars, and by extension the rest of the solar system.