Generally, no, you cannot take your phone on the slides at Siam Park for safety and insurance reasons. On high-speed attractions like the Tower of Power or Singha, loose items—including phones, cameras, and even loose jewelry—are strictly prohibited as they could become projectiles or get lost in the water systems. However, the park is very "social media friendly" and provides free Wi-Fi throughout the grounds. If you want to capture your experience, the best solution is to use a GoPro or waterproof action camera secured with a high-quality chest harness or head strap, though even this is subject to lifeguard approval on certain slides. For standard phones, it is best to leave them in one of the many secure lockers available for rent. You are, however, perfectly welcome to use your phone at the Siam Beach wave pool or while relaxing in the VIP cabanas to capture photos of the stunning Thai-themed surroundings.