A Phase DB connects to the hasselblad via a cable. The easy way to think of this is that the digital back is a strobe connected to the wrong side of the camera. The DB is attached to the camera just as if it were a Hasselblad film back (A12 or …)
After attaching the back to the camera, insert the cable into the back, then attach the small connector end into the lens to the “strobe” connector socket. You’re done. (step one) (next step)