I can kinda see where the issue is coming from though. Many students, at all levels, do not have a positive attitude towards nudity. They see it as something embarrassing or sexual. This is where the motivation for the cell phone comes in.
Say there is one member of a wrestling team who is kind of a bully to the others. Say that the team is weighing in, and the wrestler (who I shall call A for abbreviation's sake) decides to do a naked weigh-in so that he is certain that he makes the weight. If the other members of the team are there and they have their cell phones, who's to say they won't take pictures of A naked to get back at him for all of the hard times he gave everyone. Then the pictures go to the net, causing major humilation to A, which of course is a major problem.
The other aspect is the sexual one. Say that it's the same situation above, but instead of the team being present, it's just the staff working the weigh-ins in private. Say one of the staff members (B) is a little bit twisted and sick, and decides to take pictures of A for his "enjoyment" later on. This is still a major problem.
This solution seems to be banning the wrong thing. Instead of banning naked weigh-ins, ban cell phones from the weigh-in area instead. Have the weigh-in area be secluded and private, and all cell phones must be given up at the door. The team would then weigh-in together, and if someone needed/wanted to weigh-in naked, then they could have a screen to provide privacy for the wrestler weighing in.
To use
@NatureForever 's reference above, I feel like banning all cell phones from the weigh-in area would be like chopping down only the dead trees while saving the rest of the forest. Unfortunately, all the trees are already dead because of the fire.