The astrodynamics of the Mars-Phobos system is a subject that has been challenging many scientists, once this system presents peculiar characteristics which do not permit long-term natural orbits around Phobos. Given its mass and relative position with respect to Mars, Phobos do not present enough gravity force to maintain a body orbiting itself. In this context, the present work intends to use perturbation theory to study QSOs (quasi-satellite orbits) around Phobos. Considering a system perturbed by Phobos, the model reformulated using alternative orbital elements allows the identification of perturbed long-term natural orbits in the relative motion with this Martian moon. These results are significant, once they are able to provide support for the plans of JAXA’s Martian Moons Exploration Mission (MMX) to visit the system in mid of 2020’s.