It was shot with the phone but the quipment used to support the camera and audio equipment is worth at least $15,000
also the video underwent extensive color correction, whitebalance correction, noise reduction in scenes when the shadows were bought up, though the contrast problem could not be fixed.
What this shows is that you can make a decent film with a cellphone if you have $15,000 worth of other equipment and a good post production team who can perform the needed correction and special effects.
A student in my class has that phone, the video quality is much worst indoors than on the professionally made film. On the film you can see that they were using very bright directional lights to maintain the shadows and lowered the exposure on the camera to still make it look like a dimly lit hallway. thats why the shadows and highlights are exaggerated, the camera does not have the dynamic range to offer a smooth color and luminance.
So sure you can do a good film with a cellphone but it is not practical. the main difference between a $200 camera and a $200,000 camera is image quality and depth of field
the cameras we have in our phones are much better than the cameras we had in the 60's, but guess what, there are still many good movies from the 60's
the cameras does not make the movie, the crew makes the movie.
Have a 12 year old student shoot a video of a car chase and have a professional who has been filming for years do the same with the same phone and you will have 2 completely different videos.