Long ago, JH said something about there being more video of the girls talking about stuff girls talk about. My impression was that it was from earlier on the trail, before they got onto the bridge, so I have always wondered if there is digital evidence of some kind from the north side of the bridge. Unfortunately, I don't think whatever that was (if it exists), was identifying to the killer, because if it was a clear image or something like that, then I would guess LE might have released it to help with tips. However, maybe that evidence helps place him either on the north side trail, or walking on the bridge itself, going north or south, etc. Or maybe there was an encounter. Or they made a comment about a guy in the woods. Whatever. Just guessing...
As for the phone, if we are to believe that RA is the killer, and that there really was no digital evidence linking him to the girls, then we have to believe that RA became an opportunistic killer that afternoon, out of the blue at 45 years old, already armed, who got so caught up in the crime that there was unclothing, possible reclothing, killing, moving, staging, covering with sticks, leaving signatures, etc. I personally think L's clothing was on the ground and A ended up on top of the shoe and phone by happenstance, and the killer simply didn't see them or wish to retrieve them from under her body when he gathered the other clothing and tossed them in the creek. It doesn't seem a teenager's cell phone would be of any significance to him in his mindset, especially if he had no idea he had been filmed. JMO.
ETA: Now, if LE is dealing with the type of person who, as part of their fantasy, did take photos with L's phone, or made the girls take photos of each other, then that would be a definite signature and add to the enigma that is RA. In RL's affidavit, the FBI agent did suggest that this kind of killer would take photos to memorialize, and that was their cause to collect digital evidence. Would photos on L's phone be included in that PCA? IDK. Maybe wouldn't have to be. I would still be shocked if this took place, though. JMO.