How do phobias differ from fears?

Fears are emotions that come and go. They get lighter with time and pass.
But phobias are fears that are deeply entrenched in the human mind which remains in the mind more or less permanently.
Psychiatric treatment may be required to remove phobias.

By definition there is little difference between a phobia, and a fear. One difference though is that a phobia is always tied to a specific thing. therefore phobia is usually used as a suffix. Phobia also has a more powerful conotation, and is often used to symbolize an irrational fear. IE: fear of tin foil

A fear of the dark would just mean you could walk in it, but you would shiver or have bad thoughts about monsters, or whatever is causing the fear. You would just feel uncomfortable.
A phobia is when they will do anything to avoid even looking at a dark room, and almost get a heart attack when they go in the dark (it's just an expression, don't take it seriously.)

There's not a huge difference, but I think it's more the fact that a fear is a fear of something that's a common fear that a lot of people can tend to have a fear of and a phobia is a fear of something that most wouldn't fear, it's more of an extreme fear to something unusual to most.

Sometimes people are labeled as "Phobic" when they do not actualy "Fear" the root word of the Phobia. In fact I dare say it is those that label the "Phobics" who hold the fear...

Phobias differ from fear in a few different ways. Fear is a normal response to genuine danger. With phobias, the fear is either irrational or excessive. A phobia is an abnormally fearful response to a danger that is imagined or is irrationally exaggerated. Psychiatric treatment may be required to help lessen the effects of phobias.