We compare and contrast the dissipative properties expected for two models of Phobos, the mysterious irregular satellite of Mars, target of the upcoming Phobos-GRUNT mission. These models are based on different scenarios for the origin of the satellite implying distinctive internal structures. We show that the presence of hydrated minerals and water ice can significantly increase tidal dissipation. In contrast dissipation in a rubble-pile subject to low tidal stress appears to be limited. Hence, it should be possible to constrain Phobos' interior and composition from accurate measurements of its dynamical properties.