Don't put your phone in a gym locker, people are stealing and then using the stolen phones to get into other lockers

I work multiple gyms and have seen a large uptick in this. It's slowly becoming the norm and is making me question society. There was a post asking for multiple codes and a woman said she doesn't get why it's a problem, she's being "honest" by only stealing cash (there's video of her getting into multiple lockers) and leaving other items.