A host of tributes have already been paid to 27-year-old Philippa, who will be laid to rest following her funeral service on Wednesday afternoon.
"We may appear strong today but, believe me, we're not. Our hearts are breaking," her mum Dorothy told UTV, speaking publicly for the first time about the tragic loss.
"Many other people who have lost loved ones will know how we feel. We are devastated."
Dorothy and her husband, Philippa's dad Mervyn, were actually on holidays in Las Vegas to celebrate her 60th birthday when the fatal crash happened in Londonderry.
The stolen vehicle ran a red light and struck the unmarked police car. Phillipa was killed instantly, while two other officers were also injured.
The news was broken to Mervyn over the phone, in the early hours of the morning they were due to travel home, by another of their daughters - who didn't want them finding out via Facebook.
That left him to tell his wife what had happened.
We're a close family, that's just how we are ... Now one of us is missing.
Mervyn and Dorothy Reynolds
Recalling the devastating moment, when he still couldn't believe it himself, he told UTV: "I just went over to Dorothy and said: 'We've one less daughter'."
Philippa had been in the PSNI since February 2011, when she quit teaching to accept a place in the police training college. Throughout her career, she was based at Strand Road station in Derry.
"She'd enjoyed every minute of her career and, from what I hear, people think she was going to go far," her dad said.
"To hear from her senior officers about people coming from parts of Derry that would never have walked into a police station before and handing in sympathy cards, Mass cards ... It's amazing."
Speaking about the love and support shown to the family from Philippa's colleagues, her mum added: "I'm just so proud of her. She's my wee girl, our wee girl, and it's lovely to hear her colleagues speak so highly of her."
Philippa's parents remember her as a home bird, but also cheerful and outgoing - someone who concentrated on doing a good job and who treated everyone the same.
And most of all, they remember her big smile.
Whether as a three-year-old beaming for the camera during a Girls' Brigade display, or as a young woman struggling to stay serious for her official police photo, they remember that smile.
"That's how I'll remember her," her dad said.