I don’t think fear has been explored or considered for the game yet. I’m curious to see how that might be implemented, but at the same time I’m a bit skeptical of how it would mesh with the rest of the game.
There are some enemies (or at least one) that give a morale penalty (I think) if your character makes eye contact with them, but that’s more being horrified than being terrified. You might have nightmares about it, but you can still kill it with fire.
If someone with severe arachnophobia was faced with a giant web spider, they would go ballistic. They probably wouldn’t even be able to fight anymore.
Just imagine what someone with acute entomophobia would do when faced with an anthill. I’d say that’s basically game over.
Someone with strong nyctophobia caught unprepared when the sun sets would probably be completely paralyzed and likely have a full meltdown long before sunrise.
I’m not sure these would be very fun, and just making them morale penalties is a little shallow. You’d have to get creative and find a middle ground.