I've wanted to build this myself for a long time but couldn't figure out how to overcome the spicy pillow problem.
Maybe I'm barking up the wrong tree, but I thought it was risky to leave a phone plugged in all the time. Does it need to be a modern version of Android OS that has the smart charging that stops at like 85%?
>I thought it was risky to leave a phone plugged in all the time
I have had phones on a charging dock for long periods. No issues.
Unless you have some budget small brand phone that was too cheap to be true, most phones are fine plugged in.
The safest option is probably to remove the battery and run the phone from a (well defined/build) external power source, e.g. like this: https://yaky.dev/2022-09-06-smartphone-without-battery/