I wonder how practical it would be for a spacecraft to visit both moons of Mars on the same mission. Areostationary orbit lies between the two moons, and GEO is demanding to reach from LEO.
Assuming coplanar and circular mars orbits, going from 9378 km radius to a 23459 km radius orbit takes about .75 km/s.
Tack on a little more since the moons aren't quite coplanar. Also tack on a little more for rendezvous delta V. So maybe .8 km/s.
The Vis Viva equation can be used to to determine circular orbit speeds as well as the periapsis and apoapsis speeds of the Hohmann transfer ellipse.
According to this delta-V map it requires at least ~1.5km/s to get from one to the other through an intermediate orbit, so as HopDavid notes, there's a shorter direct path.
That's a substantial maneuvering investment, but less than getting a lander to the surface of Mars (let alone back up), and it could be done with a very lightweight lander.
I'm sure others will provide Hohmann numbers, but if you happen to be using low-thrust propulsion that requires spiraling down, the delta-v approximately equals the difference in Phobos and Deimos's orbital velocities, so about 800 m/s.
This is a theoretical limit for very low thrust and very long transfer times, many hundreds or thousands of orbits during the spiral, as discussed in a little more detail in this answer.
However, while Deimos' orbit is nearly circular, the orbit of Phobos has an eccentricity of about 0.015, so some additional details need to be considered - was the starting orbit a circular flyby at Phobos' periapsis, or a matched ellipse for example. These would have a small additional impact on the delta-v needed.