I wonder if it makes sense also to deorbit Phobos (instead of exploding a thermonuclear device on the surface per Elon Musk suggestion). The resulting series of collisions might release enough CO2 to create a denser atmosphere.
May be a bunch of solar-powered rail guns ([0]) to fling a fraction of the Phobos mass into space.
Now, to feel the need to install something like this on Phobos - is beyond our means, as a species.