Yeah, for some use-cases the Django Admin and everything-spawns-from-the-model approach can go from nothing to CRUD in a ridiculous time.
Phoenix is ludicrously quick to get from zero to realtime UI and interesting backend work such as polling, consuming updates, sharing state, collaboration.
Having done a bunch of Python I wouldn't discount Django but I would pick Phoenix almost every time at this point. The initial burst of Django doesn't seem like a long-term upside and Elixir/BEAM/Phoenix has a lot of long-term upside in my eyes.