Normally phosgene isn’t quite that deadly. If you catch it full concentration then you’re in for a bad time as your lungs start blistering but that definitely isn’t something that happens from a small leak unless its also in a confined space. I’ve gotten a face full of phosgene a few times on the job and you definitely notice it. Idk what it smells like because to me it just smells like pain. It feels like you just took a huff off a bottle of drain cleaner. If you get hit with enough of it, it’ll leave you short of breath and your chest burning but the only time I ever got hit with that much was the time I took a plasma cutter to an old refrigerant can I had forgotten to purge with nitrogen first while working in a closed garrage.

Suffice it to say, you would definitely know it if you got exposed to any significant amount of phosgene.