It uses a Teensy 2.0. You can see the pins for the Teensy sticking through the board around the “Phantom” text.
I think the Phantom is a nice way to get into keyboard making/modding. It’s easy to work on, supports a bunch of layouts, and programming can be done with a few clicks. Cheaper to just buy a TKL though.
$32 for PCB + $44 for plate + $10 for stabilizers + $10 for diodes/resistors/LEDs + $25 for switches = $121 without caps or a case.
Another option would be something from Winkeyless.kr. Most things come pre-soldered and they make cases for each PCB they make. Might even be cheaper, too!