All this dwelling on my own fears brought me round, as most things do, to my characters. One of my current protagonists has been through a huge trauma and as a consequence avoids crowds. As her emotional state stems directly from a major plot event elsewhere in the book, it isn't too difficult for me to remember it exists. The inconsistency should she suddenly feel at home in a packed shopping centre would be striking and any readers I hope to have would instantly lose faith in me. I'm not saying it has to be a feature of every trip into the outside world for her, but it needs to crop up whenever the unexpected does. For the most part she can regulate her response as long as she knows what's coming.
One book I dip in and out of as my work dictates is the fantastic Writer's Guide to Character Traits. I'm fairly sure I've mentioned it before on the blog because it's a really helpful book to refer to when you're unsure of how a given character may react. The section on phobias is brief but does give several traits as starting points for exploration of character. As with most descriptions in the guide, it's a platform to jump from. If you know your characters well enough then you can fill in the rest of their symptoms for them.
There are a couple of things I'd cautious about though. When looking at a blank character sheet you might get the urge to fill it up by tossing in a debilitating fear or two. Beware: these are things that will affect your characters. If you include it, if you mention it, be sure to follow it up. The second point relates to the first: although not everything about your character has to be fuel to your plot, phobias are one of those things that cause an obstruction in some way or other. If your character's phobia is barely pertinent then perhaps it can be discarded.
And, just for the record, if you want fireworks, make someone with a needle phobia go for a blood test. The results are hilarious, in a dark kind of way.