How many iphones does it take to equal the processing power of a modern desktop with a beefy GPU? Well, we can try to guess. An iphone has a 5 watt charger. A decent desktop has a 500 watt power supply. So, probably about 100 iphones = 1 desktop in processing power.
Also, it would only be working on the iphone when the game is running. A desktop is instead running it all the time. So, assuming the iphone user plays 30 min a day....that's 4800 iphones = 1 desktop.
Honestly, I don't see the point of this.
This isn't a good way to look at it.
Wattage in no way indicates processing power--- or, at least not in any sort of linear fashion. Desktop parts require much higher voltages due to higher clocks and deeper pipelines, which ratchets wattage up very quickly without similar increases in performance.
Just ask any overclocker-- they'll tell you how quickly their wattage increases once they start using higher voltages.
We can actually compare CPU performance pretty easily-- Geekbench scores are available, and they tell a pretty different story... a 5S scores 1400; about 1/8th the performance of a new MacBook Pro (which has twice the cores and four times the number of threads). Alternatively, you could compare it to an only-about-ten-percent-faster dual 1.8 GHz G5 from 2003-- which had a 604W PSU.
However, a quick glance at information on BitMining, and you see the GPUs are what are utilized nowadays, not really the CPUs.
GPU comparison would be a mite more difficult; however, as the 5S's GPU is only capable of 76.8 GFLOPS (and modern GPUs are capable of >1 TFLOPS), this would indicate that in terms of raw, peak theoretical FLOPS performance, it's capable of maybe 1/15th to 1/30th of modern midrange-highish end GPUs.. not in SLI. (GFLOPS is, on the other hand, a damn near meaningless metric...)
On the other (other...?) hand, far fewer people are buying desktops these days, and even fewer are gamers buying dedicated GPUs-- and then, only a fraction buy high-end or even multiple high-end GPUs. This is-- and has always been-- a niche market. Maybe not as niche as two 3dfx VooDoo II's in SLI, but still...
Hundreds of millions of iOS devices exist... there aren't hundreds of millions of people buying desktop GPUs-- growth has been slowing for a while now, no thanks to Intel's ever-increasingly powerful integrated GPUs (Iris is seriously formidable now), and the popularity of tablets and smartphones as gaming devices.
Anyway, I wouldn't be so immediately dismissive of the power of iOS devices. They're more powerful than you think. (And using Watts is really not a good way to compare anything.)