Sigh different "aspect ratio" for movies are not going to go away. There is more to why movies are shot in various aspect ratios and not just the ratio of the screen of the final product (whether phone, tv, monitor, movie theater, etc)
There are physical advantages for certain types of ratios for different types of movies (like action and such) due to the performances of how the different types of camera lens capture light and what type of lenses you are using in front of the digital sensor or the film itself.
I am talking about what is in "focus" and depth of field and so on, lots of these things are benefits of the type lenses being used, the aperture, and so on. You use different types of lenses for different types of shots you are trying to create.And while aspect ratio is separate from all of this (due to your ability to crop), it is still going to be something that influence what is going to be shot for different types of movies.
Furthermore aspect ratio also change the viewing experience for the human eye and modulating arousal levels, do you want to create an expansive world with your eyes constantly moving, vs a soft small intimate room, and so on. How the eye moves with saccades (rapid movement of the eye between fixation points) is partly influenced by what you are showing on the screen, and you can do different types of fixation points and movement when you have different aspect ratios to play with in the movie. For example our eyes use "saccades" to "jump / jerk" from fixation point to fixation point, while we use "smooth eye pursuit" for movements that are more constant and predictable. Aka the difference between velocity / speed (1st derivative of position in regards to time) vs acceleration (2nd derivative of position in regards to time) vs jerk also known as jolt, surge, or lurch (3rd derivative of position in regards to time).
While not visual you can easily tell the difference between these 3 things with touch / proprioception (the internal sense of movement) with unanticipated speed bumps on a road that cause your car to "jump" causes different changes of arousal compared to just the car moving in general or it speeding up or slowing down due to the brake and gas. There are similar things that happens with your arousal level and vision.
Well different aspect ratios give directors and film makers more freedom and more control, thus you are still going to see this no matter what type of ratio phones decide to adopt.
Remember, aspect ratios is not just about oh the final product you are going to watch the movie is going to be displayed on a phone, or a tv, or a movie theater which does X ratio naturally without black bars. How the movie is made, and what the movie maker wants you to feel is part of why certain decisions are made.