Just a quick question regarding Neptune. Because Phobos is spiraling in towards Mars, Mars' rotation speeds up. Does the same thing happen with Neptune's rotation?
In short, the answer is yes -- because of the conservation of the angular momentum.
The orbital angular momentum scales as the square root of the semimajor axis. Therefore, if the satellite's orbit is shrinking, the orbital angular momentum is getting smaller.
Had Triton's orbit been prograde, I would have said that, to compensate for the said decrease in the orbital angular momentum, the rotational angular momentum of the planet must be increasing (i.e., the planet must be rotating faster).
However, Triton's orbit is retrograde. So the sign of the rotational orbital momentum is opposite to that of the planet's spin. (To simplify things, I am neglecting the inclination of the orbit on the equator.) In this situation, our conclusion will be opposite: to compensate for the decrease in the orbital angular momentum, the planet must be rotating slower.