Unless your phone has full mainline kernel support (pinephone, librem 5, pocophone f1 etc...), All these Linux on phone projects
mostly use Android system services (init, surfaceflinger, rild etc..) to talk to the device hardware, without bringing up the Android UI.
They do this so that they don't have to reverse engineer and write the hardware drivers from scratch and simply use Android's user space drivers for them.
I haven't been involved in that domain for a while, but it basically meant reusing the contents of your device's /system and /vendor partitions and simply installing the Linux OS into /data.
