When she was young, she had curly hair, something her elder sister envied. She also shared their father's clear gray eyes. When she was five years old, their father took Kathryn to the Mars Colony – Phoebe wanted to go too, but was too young. She was allowed to play with some of Kathryn's PADDs instead.
When she was eight, she played a prank on Kathryn by putting a long coil of polymer into a cylinder of sun protector before one of Kathryn's tennis matches.
By the age of twenty-three, Phoebe was a free spirit, still in school, and studying fine arts and painting. Her hair had grown into a thick mass of dark curls, and she radiated enthusiasm. She had a dog, Blanca, a fluffy Samoyed mix, and it gave birth to four puppies, two male and two female. Phoebe offered one of them as a wedding present to Kathryn and her fiance, Justin Tighe. When Justin hesitated, Phoebe questioned how he could love Kathryn, yet not like dogs, upsetting her sister.
After the deaths of Justin and Edward Janeway, Kathryn took to her room and rarely got out of bed due to her mourning. Three weeks before Kathryn was due to report back to Starfleet, Phoebe took it upon herself to get her sister back to normal, going so far as to dump a gallon of ice water on her bed to rouse her. Phoebe took her sister out walking and spent a lot of time with her over the next few days until her mood improved.
In June 2380, after her sister's death, Phoebe reflected on how their father's death had brought the sisters much closer than they'd ever been, and how she had never given up her sister or USS Voyager up as lost and dead. She also remembered their reunion upon Kathryn's return.
At Kathryn's memorial, Phoebe reflected on the white pillar Starfleet had build to commemorate her sister and thought to herself that it was very phallic for a female office, and also felt that her sister would have hated the fuss. At the memorial, she spoke for her sister, stating that while Kathryn would have accepted her death in the name of duty, Phoebe could only see the death as a necessary evil so that the rest could continue to live. She told the assembled Starfleet officers that it was their duty to ensure that Kathryn's death was not in vain and that she needed avenging, and told them not to forget how she lived or died, finishing by stating "Do not take 'no' for an answer. She wouldn't have."
In 2375 a Nacene attempted to infiltrate Voyager's crew in order to acquire an artefact that Janeway had recently been entrusted with, altering the crew's memories and perceptions so that they perceive her as Phoebe Janeway, the crew's memories including the fake information that Phoebe had been commissioned to do a portrait of the Badlands and had thus requested to accompany Janeway on her mission there (Janeway later reflected when the deception was exposed that she would never have taken a civilian on such a dangerous mission). However, her attempt failed when Harry Kim and Naomi Wildman proved immune to the tampering as they originated from the duplicate ship created in 2372, making them slightly 'out-of-phase' with the rest of the crew. (VOY - String Theory novel: Fusion)