It looks like the phosgene story can be traced back to a BBC report that the Been may have either retracted or sent down a memory hole. Can’t find any confirmation on the use of phosgene.
I used a search engine to find a repost of this story in its original form.
https://sunnewsonline.com/heavy-security-in-france-as-anti-government-protests-begin/
The 8th paragraph as I see it has the phosgene reference.
As I posted tonight, the low casualty figures don’t seem to confirm the notion that phosgene was used.