What's the difference between (the mythological) Phobos and Deimos?

[Erusiel]

Mars’ moons, Phobos and Deimos, are named after two sons of Ares, who would often ride with him into battle. From his name, it’s clear that Phobos represents “fear” of some sort. But when looking up Deimos, similar concepts turn up.

As I look around on various websites, there seems to be a bank of single-word identifiers used to describe them: “fear”, “terror”, “dread”, “panic”, and the like. Most of those just sound like synonyms to me. And it also seems that when one site picks one term for Phobos and another for Deimos, another site might swap them.

So what’s the difference between Phobos and Deimos? Different amounts of fear? Different types of fear? Or are they essentially identical?

[aldiboronti]

No authority given for the references here, and William Smith’s Mythology for once has little to say, but some differentiation is offered so, for what it’s worth:

DEIMOS (or Deimus) was the god (daimon) of fear, dread and terror, and his twin-brother PHOBOS (Phobus) of panic fear, flight and battlefield rout. They were sons of the god Ares, who accompanied their father into battle, driving his chariot and spreading fear in their wake. As sons of Aphrodite, goddess of love, the twins represented fear of loss.