If your phone feels warm when using Camo, it's nothing to worry about. In order to keep your computer as fast and cool as possible, Camo offloads its processing to your phone. Over time this can make it warm — though not as warm as the inside of your computer!
We've left test phones running Camo for weeks at a time, and regularly sat on 13 hour Zoom calls running Camo without problems.
All iOS devices are able to manage themselves as they warm up, and they shouldn't get too hot. However, while the vast majority don't struggle with overheating, we've found a small percentage of problematic devices get warmer over time, just like DSLR and mirrorless cameras do. These problem devices can get warmer until they eventually display a temporary thermal message. If this happens there's no risk to the phone, but it is inconvenient.
If you have one of the few devices that does this, please let us know. In the meantime, there are a few tips you can use to prevent it:
Ensure "Screen Curtain" is enabled under the Advanced menu. That will reduce power and heat use from the screen.
If you're using an iPhone 5s, we'd recommend sticking to 720p. The 6s and above handle 1080p well.
Combining zoom / crop and image adjustments adds extra load. If the phone is warm, it might be worth disabling these.
"Portrait mode" takes quite a lot of processing on the phone, and can generate extra heat.