Imagine the iphone x, if you removed the battery and the screen, it would be tiny. Imagine 10 of these working in a cluster, a powerful machine in the size of a phone, they probably wouldn’t even need a fan. Also, cpu’s and gpu’s are tiny (only the chip, not the whole thing) why wont anybody make a cpu with titan x intagraded graphics and a large powerful cooler?
I think, the average time it takes for an iPhone to throttle due to heat when gaming is around 15 minutes. Ten of them in a compact package would be unrealistic, without active cooling. The performance gain from parallel coupling several of them would probably also be irregular because how specific code has to be for parallel computing,. Compare with how that works using SLI graphics, extremely hit or miss. Also, the GPU on an iPhone is nice though, it's just not anywhere near desktop graphics.