A stolen 4x4 crashed into the 27-year-old's unmarked police car which was on a routine patrol in February.
Philippa, who was a backseat passenger, died instantly. Two of her colleagues were injured.
Her family and PSNI colleagues organised the remembrance service in the city in which she died.
The event, which took place in First Derry Presbyterian Church on Sunday afternoon, was open to the wider community.
The late officer's father Mervyn said that his daughter will always be in their memories.
"Our baby is no longer with us."
He added: "What I hope for is that, because of it [Sunday's service], the police will be seen in a better light and that people will work with them and not hide from them."
PSNI Chief Constable Matt Baggott, who attended the service, described the young officer's death as a "desperate tragedy".
"When you lose a colleague like that, it's very sad indeed."
He added that the PSNI were determined to make the city a success in memory of Philippa.