Bleeding Freddy is a Freddy Fazbear Suit that the Phone Guy was stuffed into after Night 4 and was brought back to life due to The Joy Of Creation. (AKA soul possessing a suit)
After getting stuffed in a suit the band treated them as a new part of the "club" despite not taking him to any shows.
The Phone Guy soul went insane inside the suit and his favorite thing to do to his victims is to make them think his is Phone Guy by talking to someone in another part of a room and then stuffing them into a suit.
The reason he is named Bleeding Freddy is because of the blood streaming down the mouth and eyes.
Some people claim that when they stare into the eyes long enough they see movement and hear breathing.