Literally just get a USB cable that is designed to interface with the printer. Whatever the printer uses to interface with a raspberry pi - just plug it into your phone and there you go. I don't know what you use to connect your raspberry to your printer. Is it USB? Then connect that to your phone the same way. Is it that one weird set of pins (GPIO I think?) - then get a GPIO to USB connector.

The burden of proof isn't on me; this isn't an official Lincoln Douglass debate or cross examine debate. It's just a conversation. I hacked my PS3 with a TI89 a while back. Because the TI89 provided some code that emulated a factory reset dongle's output.

The PS3 didn't care what was providing the code. It just wanted to receive the code. I could have done that with a PC. A phone. A raspberry pi. A custom made dongle. Maybe even an analog to digital signal piano if the PS3 didn't time out on my inputs.