This question already has an answer here:
Thinking back to the original Star Wars trilogy, the Empire did not seem to have any high ranking female officers that I can recall, or who were intrinsic to the story line. The Rebels had Mon Mothma and Leia Organa to name at least two, not counting pilots or other lower ranked officers or civilians. I don't recall any female Star Destroyer captains or admirals.
In The Force Awakens, Captain Phasma is clearly fairly highly ranked within the First Order, which is a departure from the overwhelmingly male senior officers within the Empire. I'm aware that in the extended universe, there are a number of Dark Jedi, and even the Emperor's Hands (such as Mara Jade in Timothy Zahn's Thrawn series), but they aren't necessarily within the direct chain of command.
So my question is, Is Captain Phasma the highest ranking military female officer in the First Order?