I'm not aware of any specific "ziplock bags for your phone" that are used on Splash Mountain, a popular water ride at Disney theme parks. However, most theme parks have restrictions on what you can bring on the rides, and many water-based attractions do not allow loose items such as phones. To ensure the safety of guests, it's recommended to secure all personal items, including phones, in a locker or leave them with a non-rider before getting on the ride. If you are concerned about getting your phone wet, you can consider purchasing a waterproof phone case.