Captain Phasma is a fictional female in the Star Wars film series who was portrayed on screen by Gwendolene Christie. Captain Phasma is a senior Stormtrooper and the first stormtrooper to be identified as being a female in the films. The fact that she is chrome rather than white is a sign of superiority rather than because the character is female. Its unlikely she was a clone model version but perhaps a conscripted female from one of the many planets that the First Order is in control of. The pictures and the trailer implies that Phasma is an important character and one that is senior and is on the side of the First Order, the successors to the Empire. Phasma will be the first female character that is on the Sith side of the battle although she will not be a Sith warrior. There are females in the Empire but they have only existed in the expanded universe.
You don't get to see Captain Phasma without her helmet off in the film so it is a little disappointing to to have a "groundbreaking" character and not to actually see her face. She is the commanding officer for Finn who admonishes him for taking off his helmet when Stormtroopers are not allowed to do so. As we didn't see Phasma without her helmet, it created a bit of discussion and argument on the internet. A future film should she appear in will probably see her without her helmet.
In an interview, Gwendoline Christies confronted this and responded. She thought it was better to not see the character face and not to judge her on what she looked but to judge her on her actions. ref: EW.
The last we see of Phasma is when she is forced by Finn and Han Solo to drop the shields so that the Rebel Alliance squadron led by Poe Dameron can attack and destroy the Starkiller Base. Her survival is unclear as to her future.
Captain Phasma appears briefly when Finn and Rose Tico sneak into Supreme Leader Snokes space ship to deactivate the tracking device that is preventing the Resistance from escaping the First Order. Finn gets to face off against Phasma once more. Phasma falls to her apparent death but her death is not assured because it depends on her body armour and wether it will be enough to protect her from her fall.
Captain Phasma is still not shown without her helmet off. There are a few more females on the First Order side but none are as iconic as Phasma. Captain Phasma's helmet breaks but it doesn't reveal her face, only her eye. Phasma doesn't have Force powers and isn't able to probably save herself.
There is no background in the films that relate to Phasma. Phasma is just a secondary character, one that is not part of the plot but one that is a bonus to the story. Captain's Phasma' background will be filled in by a spin-off story book but unlikely not a film.