I largely agree, but wanted to add a few data points about power usage.

5.5 Watts:

My Dell XPS13 with a bunch of browser/slack/java processes on Linux. (it's below 4W at idle)

40 Watts:

My 6-year old Xeon E3-1230 (v1) with 14TiB usable ZFS and 32GB of ECC RAM.

Also, if you're really going for very low power, I'd suggest an RPi Zero W instead of some Android phone. $10 @ MicroCenter and you can install pretty much anything your heart desires from standard Raspbian repos. I can't even measure it's wattage at the outlet with my power meter.