Active cooling would probably work — something like a fan blowing directly at your phone — but I don’t think changing the ambient air temperature will be sufficient. (Unless the change is enormous, like recording outdoors in the winter.) Also, make sure your phone is not in a case. Of course, you could always record lower quality video. But that’s not really a solution.
Like I get it needing to stop.
I tried the other camera route, the lower light performance was abysmal. Now I was going for a higher end webcam route that was good for YouTube. But it was shockingly bad compared to my iPhone. And I have a good amount of light, it was just that grainy look on blacks that really bothered me.
I am also just not really in a position to spend over $1k on a camera when for the most part my phone works if I could just get past one pesky little detail.
Related question (if you see this). I have started just cranking down the AC when I need to record something. Since annoyingly the iPhone will just stop recording with no notification. So if I have my phone mounted I may just loose some recording. Have you found a solution to this by chance?