I agree, charlatans like Carl Sagan claimed that Phobos was hollow and therefore artificial, while it is merely low-density, a kind of mineral foam, and in the distant future will cover Mars with a deep crater field caused by the ejecta when Phobos crashes into the Martian surface.
The striations on the surface do make it and many other asteroids look like they were strip mined. Its a cool thought but the most likely explanation is natural.
Carl Sagan never claimed Phobos was hollow or artificial. You’re thinking of a colleague of his, Joseph Shklovskii, who wrote ‘intelligent life in the universe’ which Sagan edited to the point of becoming co-author. Sagan himself was an extreme UFO skeptic.