Meet Screenholder by BunkerWall: a 17-pocket shower curtain liner that can hold your phone, tablet, and other comparable devices. Measuring 72 x 72″, this is completely waterproof and lets you put your phone at different height levels. You can use it to interact with your phone while taking a shower.
Due to its size and weight, Screenholder doesn’t require magnets at the bottom to resist sticking to you. Pretty affordable too. More info is available here.