Cell phones as functioning devices wouldn't survive the crash. It is not even required of black boxes. What is required is that the memory in them remains readable in a lab. The same can happen to cell phones. Their entire solid state memory is a single Flash chip. It is not protected by the metal as it is done in black boxes, but short of being broken in half that silicon is pretty hardy. It may be that memory of some phones could be read. But will they even find them, if they can't find the second black box? And it's not like all passengers would be witnessing the attempts of the pilot to reach the controls. Probably only the first class - and would they, serious and busy people, be making video of that?
But calls, texts, or videos could have been sent from the plane and made it through to recipients. A lot of information via phone could have been transmitted in 8 mins.
I'd bet that once passengers realized that a pilot was locked out of the cabin and that the situation was very unusual, that some number of passengers started recording with their cell phones. But the odds of finding them and playing back anything. Who knows.
Like Jerry Seinfeld said about crash helmets for parachutists, if the chute doesn’t open, that helmet is wearing you for protection. Those phone are protected by lots of soft tissue. Flash drives inside a phone in the pocket of a human have a good chance of being readable. They just have to find them among the debris spread out around those windy hills.