Joaquin Phoenix All Smiles as The Joker in Action

Joaquin Phoenix keeps giving us a little more as The Joker -- this time he's in full costume as The Jester of Genocide ... and he's all smiles about it.

Check it out -- it's the first look at Phoenix in makeup on set as the notorious villain of Gotham City. The filming was going down inside an NYC subway station in Uptown, Manhattan. You see The Joker get off the train in a mask ... which he really didn't need.

As we reported ... Joaquin's "Joker" look was revealed Friday by Warner Bros. in a short promo, showing the transformation from Arthur Fleck to the Clown Prince.

But, even when he's just Arthur ... he's still pretty creepy.

This flick is an origin film about Batman's archenemy. Announced costars include Robert De Niro, Zazie Beetz, Marc Maron and Bryan Callen. Martin Scorsese is producing and Todd Phillips is directing.