I guess the author wants me to hate Phasma because she killed her tribe, her parents, her brother, etc to get to the top of the food chain in the First Order.
But Phasma's so one-dimensional and BORING. She never really comes across as evil, just... dullsville. Maybe the author thought giving Phasma any other depth would accidentally make me like her? And then I'd feel bad for liking a monomaniacal murderer?