Amnesty International NZ says the amnesty does not go far enough because scores of peaceful activists will remain behind bars.
Mr Blackwood's mother, Angela Blackwood, said the family were "absolutely delighted" at the happy but unexpected news that Philip would be freed.
"It's come as a shock -- we weren't expecting it.
"We're still a bit shell-shocked at the moment and we're just waiting to hear when he will actually be released."
Mrs Blackwood said the family had been told her son could be freed within 24 hours or up to a week.
"Obviously, paperwork should be cleared. The Myanmar Government has still got his passport."
She said the family had visited their son last June. That was the only time they had spoken to him directly, she said, as he was not allowed a phone.
Mrs Blackwood said the New Zealand Embassy and her son's fiancee had updated them on his condition in prison.
"His fiancee, who still lives in Myanmar, sees him every two weeks.
"She gives us regular updates about his condition and also, whenever she goes, the embassy officials visit as well and they give us a very detailed update on his condition as well."
The Ministry of Foreign Affairs and Trade (Mfat) has confirmed Mr Blackwood is on the Burmese presidential amnesty list.
"This is, understandably, of significant relief to his family," a spokesman said.
"Mfat -- through the New Zealand Embassy and consular staff -- has been providing consular assistance to Mr Blackwood and his family since his first arrest and detention."
Amnesty International NZ Burma researcher, Laura Haigh, said although her organisation was delighted for those who will walk free, "scores more remain behind bars, while hundreds of other peaceful activists are on bail facing jail time".
Ms Haigh pointed to the case of a local peace activist, Patrick Kum Jaa Lee, who has been sentenced to six months in prison for "online defamation" for a post on Facebook showing someone stepping on a photo of a local prominent military leader.
Ms Haigh said the proposed releases "perfectly sum up how the Myanmar authorities give with one hand and take with the other".
"Just hours after the prisoner amnesty was announced, an activist has been sentenced to six months in jail for nothing but a harmless Facebook post."
