Star Wars: The Force Awakens - who is Captain Phasma?

As the shiniest of characters, the most reflective of all Star Wars characters, and a Game of Thrones actress to boot, Captain Phasma has our attention. We've been wondering what the backstory is on this character since we first heard the name - and now that we've seen Star Wars: The Force Awakens, we're still wondering. The film itself doesn't …