In an interview with IndieWire, cinematographer Lawrence Sher discusses shooting the scene and how it completely mesmerized everybody on set that day:

This isn’t the first time we’ve heard about Joaquin Phoenix’s improvisations on the set of Joker. Previously, Todd Phillips talked about how the poetic bathroom scene dance in the film was initially supposed to be something else entirely. In the IndieWire interview, Lawrence Sher talks a little bit about the scene. Joker is currently playing in Malaysian cinemas. 

Joker Crew Was Mesmerized as Joaquin Phoenix Randomly Improvised Refrigerator Scene - 46