Doesn't really help but I've used this a few times
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I taped my phone to the tank which actually worked pretty well until I got off at my destination and peeled the tape off and managed to drop my phone on the floor and cracked the screen
The ex. used hair scrunchies....which worked great for her....soft case on the holder, then phone, then secure it. Then everything comes off and goes back.....even the scrunchies, which she couldn't really wear with her lid on.
You could try looking at some mic. stand options....there's a ton out there. Or surfboard apps....??