Brad Hargreaves said he saw the missing teenager's feet
slide on rocks during a call at around 8.30am, saying that is how he knew Mr Slater was not on a road.
He then said Mr Slater went down a "little drop" in one of his last video calls, and added: "He said, 'look where I am'.
"He didn't seem concerned on the phone until we knew how far away he was. I said, 'put your location on'. He said: '15-minute drive, 14-hour walk'.
"I don't know if it's accurate or not so I said to him: 'It's only a 15-minute drive, get a taxi'."
Volunteers with experience navigating difficult terrain were requested by police to help in the search for the missing teenager from Lancashire.
news.sky.com
*I'm not sure he got a taxi, he may have, I hope so. I do think someone did 'help' him off the mountain like his dad mentioned as a possibility.