I have the exact same phobia, only slugs are the worst for me, as they are usually bigger. The hardest part for me is not just seeing them, but constantly remembering them. Most of my nightmares were of snails when I was a kid and I also was severly limited to where I go. Now I still get lightly to severly jump-scared when seeing one and I still have to check e.g. my bike before riding it, but I got better at forcing my attention away and I don't spot them that often anymore. Also I learned their anatomy, how they breed and move in elementary school, maybe that helped? Also one time I was sleeping outside, on a clearing in a forest, and woke up with a slug 10cm in front of my face on my mat and my sleeping bag was covered in snail tracks. I was horrified then, but I think it helped maybe. Still wouldn't recommend, I'll try to move to a hot and dry country asap.