"Alignment" as in "lawful good" or "chaotic evil"? I'd say "neutral evil" because the Drow are traditionally "neutral evil" and they tremble under the tyranny of the spider queen, Lolth.

True Neutral Fear of spiders is an inate defense response passed down by survivors of spider encounters. It is a behavior accessible to creatures of all alignments. How funny would it be to have the BBEG & an arachniphobic paladin cluch eachother in fear of a wildshaped giant wolf-spider?

Quoting the wise Sage Yoda > Fear is the path to the dark side. Fear leads to anger. Anger leads to hate. Hate leads to suffering. Since darkness is traditionally liked to evil the "Dark side" is so aligned to. And Fear is thus the path to Evil leading to the conclusion that Fear, and being filled by Fear, is aligning, or being aligned to, Evil. So on the Good-Evil axis Fear of Spiders is aligned to Evil. Fear being an emotion have no intrinsic aligned towards Order or Chaos, how it affects the person is individual. Therefore Fear of Spiders (arachnophobia) is Neutral Evil.

Post-clarification answer: unaligned Most reference books have normalish spiders categorized as unaligned beasts. They don't qualify as intelligent enough to have morals & ethics.

@Shkshkshk @rpg Chaotic good. People don't understand spiders but they are so lovely and helpful. They're just doing spider stuff.

Chaotic Neutral. People freak out (chaos) due to ignorance (neutral).