This is the fraud line for Priceline. My credit card company called me before Priceline did, so I was aware there had been a fraudulent charge. Priceline verified the last 4 digits of my card (only) and confirmed I didn't make the reservation. They are attempting to cancel the reservation and refund my card.
I had my doubts when I received an email from them, but upon calling they had travel info that only Priceline would have had for reservations that I did actually make. This is a legitimate phone number.