I did it with an altcoin I was working on a long time ago. I'm not sure that eMMC/SD access speed would be fast enough but maybe modern phones with a power-and-USB3 adapter and a fast flash device with over 100mb/s read/write speed would be able to do it, memory certainly wouldn't be a problem.

Only problem is since android devices changed to USB-C I haven't seen the old school style OTG cable that lets you charge and access a client device at the same time. Maybe a phone with wireless charging would let you keep it running continuously.

Android is just a cut-down version of Linux and can perfectly fine run a linux environment inside LXC containers, and you don't need root to do it. Just the issue of power-and-storage at the same time I don't know about. An old device with the USB micro socket and the old style OTG-and-charge would be able to do it but the USB interface would be a bottleneck.