The weirdest part about the Smith story is that his connection to the whole thing has never been explained. We still don't know who shot the video, whose phone it was on, or why Smith was in that photograph.
Also, stealing Smith's phone during the shooting: that is weird. You have a beef with someone, they end up dead, you GTFO. You don't stop to grab their phone, which in any case directly connects you to the murder.
Mo trying to sell the video being stupid, well, he had no reason to believe that anyone outside their circle knew about the video or where it came from (if it deed indeed come from Smith's phone).
I am still unconvinced that Smith was killed *for* the phone but I think he is tied up in this in ways we don't yet understand. It's quite possible that he was killed because of a pre-existing beef AND he had the video on his phone, and they knew it, and took it.