Not turning over the phone makes me wonder if there were phone calls or text messages that for some reason Beth is trying to conceal. She may think she has a good reason for hiding it, and she may think it doesn't have anything to add to the investigation, but I still think the investigators should have everything.
And not turning over the camera makes me wonder the same thing. Maybe it pictures from the late nights and early mornings hanging out at Carlos and Charlies, but there could be stuff in the background that helps the investigation.
Would you turn it over with the risk of never seeing it again, knowing those were the last minutes of your child's life?