The tape heard Miles sobbing as she said: "There was screaming and screaming. Oh my God. It's awful. I went into the room and he's killed her. Oh my God. Is this real?
"There's blood everywhere and it looks like a horror film. He was using the screwdriver and stabbing."
The tape was played to the jury after CCTV images were shown of newly-freed prisoner Williams going into the "halfway house" Sirhowy Arms Hotel at Argoed, near Caerphilly, South Wales.
They also showed Miles's son, Christian, arrive with other guests outside the room. She then told him: "You are not going in there." She tells her son to come away from the door, after informing the operator that she has seen Williams eating the person inside.
The operator tells her that someone from the police will be straight there.
The operator informs officers at just after 1am that there has been a reported murder at the Sirhowy Arms Hotel where a man has attacked another person with a screwdriver and is eating the person's face.
The operator then said: "This is genuine." The operator asked to have all the people inside the hotel leave as a number of police officers would be arriving.
The hearing was told officers arrived at the hotel 14 minutes after the call to arrest Williams.
Williams, 34, was released from prison just two weeks before he killed Yemm. He then died himself after being Tasered by police.
Yemm was found covered in blood lying underneath Williams in his hostel room - after he binged on drink and drugs in the days before.
An inquest into both their deaths heard paranoid schizophrenic Williams was released from custody without any medication or supervision despite being sectioned twice and complaining of hearing voices in his head.
His mother, Sally Ann Williams, told the inquest that her son had previously been diagnosed with drug-induced schizophrenia after claiming he was a tree and saying his food was poisoned.
She said he had been placed in foster care as a teenager after being caught stealing to buy drugs, and his drug addiction was "set in" after he returned from a young offenders' institution.
His mental health "deteriorated" after he split up from the mother of his son about three years before he killed Yemm.
Williams said: "At some point he was sectioned once or twice but I don't know the details."
Williams was sent to prison for two-and-a-half years where he was given medication, but was offered "no support" when he was released on October 23, 2014.
His mother said: "There was no mental health support whatsoever. He told me he'd been released without any medication. He'd been released without licence and had no probation restrictions."
She said her son complained "the voices were back" in the days before the killing.
"He told me his head wasn't right," she said.
She dropped food off outside his hostel hours before he killed Yemm, where he "seemed fine" and received a text from him later which said he'd made "a lovely dinner" with the food she'd brought him.
That night he killed Yemm in his room, and died in the early hours of the next morning after being Tasered by police.
His best friend, Rhodri Moore, told the inquest Williams seemed fine after his release from jail, but deteriorated "after the first couple days".
He said: "He was taking drugs on a daily basis. He said when he looked at a can of Coke he could see faces.
"He wasn't very well. He was seeing things, hallucinating. He was annoyed and on edge. Depressed.
"He couldn't get any medication. His mother was trying very hard to get someone to see him. He was willing to be helped. He wanted to be helped."
He said Williams binged on amphetamines and cannabis after his release, and Williams was smoking weed the day before he killed Yemm.
Moore told the inquest: "He was looking wired. He looked to me like he hadn't been asleep."
The inquest in Newport continues.
