Theory is kinda right, but whole lotta wrong, you see the phone guy is also a night gaurd, but died in night 4 after jeremy fitzgeralds shift in night 6, and after fritz smith's shift in night 7 in fnaf 2.
Mike schmidt then at the sequel, in fnaf survives for 7 nights, this time trying to solve the mystery behind it, and also 5 kids died in fnaf 2. 1st kid died and possesed marionette, the rest died, and was repossessed by the marionette and stuff the 4 corpses into the 4 animatronics, also the 4 kids can shift to the toy animatronics from time to time too. and after the killer was killed by foxy in the bite of 87, while the killer was trying to lure more victims in a golden freddy suit, which explains the golden freddy being a real pain in the ass in fnaf 2.