Oil paint on canvas paper by Paul Burrow.
Full painting size 11.69 x 16.53 inches (Image above is cropped).
This Captain Phasma painting was done for Star Wars Destiny collectible card game produced by Fantasy Flight Games. This is card 137 from the Spirit of Rebellion booster pack. Star Wars and all related characters are © Walt Disney & Lucasfilm.
Here's the card from the game.