No, you really cannot build a smartphone. I'd really like to see you make an ARM CPU by hand, just using a silicon wafer. Or solder a modern BGA package relia

No, you really cannot build a smartphone. I'd really like to see you make an ARM CPU by hand, just using a silicon wafer. Or solder a modern BGA package reliably without a reflow oven. >and a 3D printed case That's not allowed. The requirement was for something "hand made". 3D printing is robotic, so you can't do that. You have to make the case by hand from a block of plastic with unpowered hand tools.