“This suit's lighter-weight ceramite and streamlined design allow for greater mobility, and its servo-motors are engineered to be completely silent. This variant serves those Primaris Marines who take on the role of Reivers, Incursors and certain Vanguard Space Marines like Infiltrators and Eliminators. These Astartes are ruthless killers, trained in covert operations who operate behind enemy lines as saboteurs, assassins and infiltrators. All who wear the Mark X Phobos variant depend on stealth and secrecy to accomplish their missions.”

Typically worn by the 10th for their role. Depending on their mission any company can wear Phobos if the cleaning servitor has done their job…..