Fritz Smith IS Mike Schmidt who IS THE PROTAGONIST OF FNAF3!
Mike Schmidt is fired for the same reasons, albeit with unprofessionalism added, possibly due to the fake name.
Unnamed protagonist of FNaF3 has Hallucinations, much the same as Mike does, probably due to the madness he has endured since dealing with this nightmare for years.
Phone guy welcomes you BACK on Night 1 of FNaF3.
I Think, Fritz, after surviving the tragedies and knowing about what happened started to investigate the history of Fazbears, and found out why it's been happening, tracing the horror back to the very first death. in order for him to recover, he decided he must try and stop the animatronics, so applies for the Job when he learns a new place is opening. he tries and fails to solve the mystery and save the souls of the kids before another death happens, Phone Guys brutal murder and the place is closed for good.
Then something happens. a NEW place opens, and Mike/Fritz, still dealing with the mental trauma decided this will be his last stand and applies once more, because they know he used to work there, he would act not only as a security guard, but a living flashback to the security guards that once worked there. throughout his ordeal, he sees his hallucinations frequently as burnt, because he knows what he has to do, he does the usual, survives the nights, and helps free the souls of the dead, in order to make himself better.
On the last night, believing it to be all over, he torches the building trying to end his horrific ordeal once and for all.
he escapes, doesn't get paid, and thinks he is free. Springtrap is gone.
until he sees the article in the paper and knows, just as it says in the trailer, he will have to come back....
he always does