Inquiry commissioner Ted Hughes delivered a 57-page written decision rejecting a proposed publication ban Thursday morning in Winnipeg.
Hughes said there's no evidence to suggest that publishing the names or images of social workers in the media would put their personal safety at risk.
When Phoenix's foster mother, Kim Edwards, heard no ban would be granted, she cried and hugged the people around her.
Edwards, who looked after Phoenix before her mother and stepfather regained custody, said the ruling will help people to take responsibility.
"It's all gonna break open now. It's wide open now,” she said. “Social workers are going to start acting properly in fear of repercussion or accountability."
Hughes has, however, imposed a publication ban on the identities of seven people considered as informants — people who came forward with concerns about the girl's care at various times.
The Manitoba General Employees Union (MGEU) and several child welfare authorities wanted to restrict media outlets from naming or photographing any employees when inquiry hearings start Sept. 5.
Five media outlets, including CBC News, opposed the proposed publication ban. Edwards and Phoenix's biological father also opposed the ban.
The MGEU has said it would not pursue an appeal of the decision.
Killed in 2005
The inquiry will look at the circumstances surrounding the death of Phoenix, who had been neglected and repeatedly abused by her biological mother and stepfather.
Samantha Kematch and Karl McKay were convicted of first-degree murder in 2008 in connection with Phoenix's death. Both have since exhausted their appeals.
Phoenix was killed on the Fisher River First Nation in June 2005, but it was not until nine months later that her body was found wrapped in plastic in an unmarked shallow grave.
Court heard during their trial that the pair neglected, confined and repeatedly beat Phoenix.
The girl was taken by Child and Family Services at least twice during her short life — once at birth and again three years later — but she was returned to her mother each time.
The province ordered the inquiry to examine how Manitoba's Child and Family Services (CFS) officials failed to protect Phoenix and why her death went undiscovered for months.
Could 'radiate distress'
As arguments for and against the publication ban were heard last week, the MGEU's lawyer accused the media of being "principally interested in the sensationalization of stories and the laying of blame," not in accuracy or truth.
Garth Smorang argued that showing the names and faces of child welfare staff who worked on the Phoenix Sinclair case would hurt their ability to care for children, and possibly influence their willingness to testify openly.
Kris Saxberg, a lawyer for the child welfare authorities, had argued that media coverage that names the social workers would "radiate distress through the system" and lead to increased apprehension as social workers react to the negative coverage.
But Jonathan Kroft, a lawyer representing the media outlets, said imposing a publication ban would make a mockery of the inquiry, which is supposed to be public, and set a precedent for similar proceedings across Canada.
Kroft also accused the union and the child welfare agencies last week of wanting to control public discussion of the inquiry.