Yeah that seems like a fine idea, heat is greatly reduced by having the phone case off and lie it flat on any table or flat surface.
Besides, there won't be any heat concerns routing max 10Mbps continuous (1.25MB/s ), assuming only 1 device is connected. The phone is idle and the screen is off.
Hotspot over USB or WiFi are both good options.
If you want serious security, you'd likely have to go to enterprise routers.
The only downsides I see are:
- not sure how many wifi clients you can have connected
- your phone likely is below average for wifi range.
- 2 input 2 output antennas isn't great for multiple clients
- a pixel router is on the expensive side unless this is a leftover device.
- phone permanently plugged in can cause the battery to balloon. Set 80% charging protection and have it sit at 80.
But,
- security updates and longevity are a big concern. I usually get a headache trying to find a router that is a recent release and within the person's price range. Many of the new routers are wifi 7 only or more expensive if you want a recent one. Many routers for sale are 4-6 years old and somehow still for sale and EOL soon, criminal behavior.
I'd go for if I had 1 lying around for personal use instead of spending money on a router.
Autoreboot can be disabled. Just keep an eye on the phone battery ballooning up!