https://www.froresystems.com/

This sounds promising. Dustproof. I dont think waterproofing the air channel will be necessary. This can be used as a way to create a channel for air to pass through without compromising the waterproof seal for the phone internals. The air channel can be a pass through and offers a big benefit in cooling. If there is blockage or damaged fins(I think they are vibrating fins.), then the phone will get warm and automatically throttle. A repair will not be needed unless you want the full performance. I live in the hot desert, and active cooling would be a dream come true. Every high-end phone gets hot to the touch from using GPS or streaming outside.

Edit: Another note is that most people don't beat up their phones with high-pressure water(dirty or clean). If that was the case, then the phones water seal would suffer or be compromised as they are water resistant to low pressure and may not seal against high pressure.

Thin and flat too!