Mrs Phelps, now aged 83, wrote a letter to the Bay of Plenty Times Weekend asking for help to find her relatives earlier this month in the hope that she could meet her half brothers and sisters before she became too ill to travel.
She believed her mother may have had as many as eight other children, who may not know they had an Australian sister.
"They were last heard of in Auckland, with my half-sister Francis and half-brother Leo, plus others ..." she wrote.
"I am trying to locate their whereabouts as I am now 83 years of age. I last saw my mother when she left Sydney by ship for Auckland about 1938-1939."
Mrs Phelps' granddaughter, Tamara Searant-Strachan, who is helping her with the search, said her nana had just one photograph of Edna and had carried it with her all her life.
"She feels like there has always been this gap in her life and she has searched for almost 70 years to get the information she needs to move forward," she said.
"Nana actually came to New Zealand in 1989 and spent about a week searching for her mum, but unfortunately Edna had remarried and changed her name again.
"When Edna first came to New Zealand, she was with a man called Jack Walsh, who we think she had four children with when she lived in Auckland until around 1943.
"In 1946 she got together with a man called James Francis Sexton, a Kiwi guy, and they moved to the Bay of Plenty. From our research, they lived in Tauranga in 1954, then in the 1960s they moved to Te Puke, where they stayed until around 1970 or so.
"They also lived in the Kaimai area and in Waihi, where James Sexton died in 1990. He was classed as a dairy farmer, according to the electoral roll."
Mrs Searant-Strachan said her nana was upset her mother had died before she got to meet her but was determined to reconnect with the remainder of her New Zealand family.
"The main focus for nana when she was younger was to meet her mother and find out why she left her and what happened to her," she said.
"She will not get that now because Edna has passed away, so she will not get those answers but she may get to find out what her mother was like, and meet her brothers and sisters.
"That would be exciting for her as she was always an only child.
"They are probably not even aware of nana and, yes, it is late, but it is better late than never ..."
Mrs Searant-Strachan said the rest of the family were excited to meet their aunts and uncles and cousins.
"It will be a good excuse for a holiday to New Zealand," she said.
"My nana is already talking about coming over if we can locate our family, it has given her real hope after a very long time."
If you think you can help the family reconnect, contact the Bay of Plenty Times Weekend on (07) 577 7770 or email news@bayofplentytimes.co.nz. You can also contact Tamara Searant-Strachan on 61412 778 934.