In this thread, there is a discussion pertaining to striations on Phobos. I didn't want to hijack the thread with my unrelated question so I've started this one.

In the course of that other discussion, it is mentioned that Phobos is slowly losing energy and is spiraling into Mars. My question is, will Phobos impact Mars, and if so, when?

What about Deimos? Is it spiraling in as well?

In the link on the other thread, it says Phobos will impact or break apart in about 100 million years. So mark your calendar. =)

Phobos will break up or crash into Mars in about 50 Million years.
Deimos will spiral out.

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So a moon orbiting faster than a planet rotates (phobos) loses energy due to tidal friction and comes closer to a planet. In the process it also gives energy to the planet speeding its spin up. As the moon aproaches the planet tidal forces increase eventually ripping it apart at what is called the Roche limit.

A moon orbiting slower than a planet rotates (moon, demos) gains energy due to tidal friction and spirals away froma planet. Also taking energy from the planet ans slowing its spin down.

Am i correct then in assuming that if a planet and a moon were tidally locked they would be be permanently held at the same orbit, only being slowed by friction of space dust and other fantastically small effects.

No, unless it were a planet and moon not near a star. The Sun also raises a tidal bulge on the Earth, which would, after the Earth and Moon get tidally locked, result in the Moon descending back toward the Earth (but not quickly enough to happen before the Sun turns into a red giant).

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