Unfortunately, this is completely the case. There are plenty of solutions out there that could really alleviate this headache but parks tend to go the lucrative money-making route. Although, from their perspective, it does make sense: at a dollar-a-pop, lockers likely make a big park like Cedar Point a few million in extra cash with very little upkeep costs.
Phones on rides are becoming an increasingly common problem, and not just on these airtime machines. It seems like every hotshot is trying to film a bit for their Snapchat story or get that special selfie. The past few times I rode The Beast at night, kids had their flashlights on, which detracted from the experience. There really should be something done to encourage leaving your phone in a secure pocket or in a locker or storage bin or something...but it's up to the parks to brainstorm, implement, and enforce a more desirable policy.