What would i have to do to get a doctors note for work saying i can't work around spiders?

May need to see: psychiatrist for this note if it's a bonafide phobia of yours. It would appear more credible, and verifiable. There's very few professions that you'd be exposed to spiders in reality, since they aren't often seen unless you are in the extermination business. So, realistically, it may be harder to prove it's merit if your job has no exposure to spiders. Most places are clear of these insects.