Debra Reynolds choked back tears as she paid tribute to her best friend and soul mate.
"Never in my life would I think that I had to be the one saying goodbye," she said.
The 27-year-old was killed in Londonderry on Saturday when a stolen 4x4 crashed into her unmarked police car which was on a routine patrol.
Philippa, who was a backseat passenger, died instantly. Two of her colleagues were injured.
"To know that she touched so many lives in such a short time on earth is a real comfort to us all," Debra continued, discussing her younger sister's love of nights out, shopping, movies and books.
"I'll never understand why God chose to take her from us at such a young age - when she had so much to give - and I can't imagine one moment of my life without her.
"The baby of this family is gone - my daddy's little girl," she added.
Parents Mervyn and Dorothy, and sisters Debra and Nicola, led the mourners at Mossley Methodist Church Newtownabbey, Co Antrim after a private service was conducted at the family home. The burial then took place at Carnmoney Cemetery.
The First Minister Peter Robinson, deputy First Minister Martin McGuinness and Justice Minister David Ford were among the hundreds of mourners.
Earlier on Wednesday, the PSNI Chief Constable Matt Baggott described the day as one of "profound sadness and sorrow."
The PSNI chief said she was "a superb police officer" working for the "finest police service in the world," before adding that "Philippa was, undoubtedly, the best of the best."
We will not forget her, and my commitment to her family is that we will work even harder to be the Police Service that she stood for.
Chief Constable Matt Baggott
In an emotional interview, Matt Baggott - along with District Commander Chief Superintendent Stephen Cargin - thanked the Reynolds family "for giving her to us."
"She was kind, she was caring, she was courageous when necessary, she was compassionate," he said.
Philippa originally qualified as a teacher before leaving the profession to accept a place in the police training college in February 2011.
The PSNI chief revealed how he had been the convening officer at Constable Reynolds police graduation and said she had sent ripples through people's lives.
He said she was "part of the story of peace building in Derry/Londonderry."
"Peace comes when people show kindness, peace comes when people are caring - and Philippa was part of that story."
He said that it was a "huge privilege" as her Chief Constable to be able to pay tribute to her.
"I know that today there will be huge numbers of people who have the family in their thoughts and prayers and I know they'll take some comfort in that and on behalf of the police service, I thank people for their support."
On Monday, two homeless men appeared in court in Derry in connection with the crash.
Conor Clarence, 23, and Shane Frane, 25, who are both from the Simon Community hostel at Bonds Hill in Derry, stand accused of a total of 14 offences.