I understand that drawing it thru a lit cigarette will kill a person pretty fast. Decomposes when heated into phosgene or something.
Yes Phosgene is very toxic. I understand it was used in chem weapons at some point.
http://www.historylearningsite.co.uk/poison_gas_and_world_war_one.htm
Phosgene is about 3/4 the way down. Nasty.