Rinse chicken and pat dry. Cut crosswise into 1/8-inch-thick strips 2 to 3 inches long.
Place a 10- to 12-inch nonstick frying pan over high heat; when hot, add oil, garlic, ginger, chili flakes, and the chicken. Stir often until chicken is no longer pink in the center (cut to test), 3 to 4 minutes.
In a small bowl, mix broth, fish sauce, and cornstarch until smooth. Add to pan and stir until sauce is boiling, about 1 minute. Add basil leaves and stir just until barely wilted, about 30 seconds. Add salt to taste and pour into a serving bowl.