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His brother Mark Leishman earlier said the problems were first noticed in February last year.
A tumour was removed in March and family had hoped for a recovery.
"Phil was down at a family reunion in Central Otago and he noticed his driving was a bit strange. He was doing a commentary for the NZ Women's Open.
"He was thoroughly professional of course, but he was struggling. He couldn't get the words out quite right. He went to the ophthalmologist and they discovered something there. That's when it all started."
He said Phillip was "so chuffed" to get a text from Lydia Ko's coach last week with thanks for giving her confidence behind the microphone and in front of cameras.
"He had a big smile on his face when he read that."
Longtime friend and race caller Des Coppins was Phillip's best man.
"I look at Phillip as my mentor, he gave me my start."
Leishman was a feature of New Zealand broadcasting for more than four decades.
He started his career in radio in 1970 and began working in television a year later when he went to Dunedin as a relieving sports officer, according to NZ On Screen.
He then moved to the nightly network bulletin as sports news presenter, appearing alongside the big names of TV news broadcasting at the time, including Dougal Stevenson, Bill Toft, Angela D'Audney, Jenny Goodwin and Richard Long.
In 1975 Mr Leishman hosted the New Zealand Games and began his long association with horse racing, which included hosting the horse programme Turf Talk until 1979.
In 1976 he covered the Montreal Olympics and established himself as host of the Olympic and Commonwealth Games, a role which continued until the 1998 Olympics in Kuala Lumpur.
In 1997 Leishman formed a new company called Uplink, now known as Sportinc. He was the executive producer, company director and fronted the company's popular Golf Show.
From 1991 to 1996 he hosted 1250 episodes of TVNZ's Wheel of Fortune and was host when boxer David Tua famously appeared to ask for the letter "O for awesome".
Off screen, Mr Leishman was involved with children's charity Variety since its inception in 1989.
In 2011 he was appointed an Officer of the New Zealand Order of Merit for his services to broadcasting and the community.
He leaves his wife Michelle and three children - Harry, 20, India, 17, and Lily, 15.