In a frying pan large enough to hold all the fennel, heat the oil over medium-low heat, and add the garlic, anchovies, and pepper flakes. Cook gently until the garlic has softened and the anchovies begin to dissolve. Add the fennel and continue cooking, stirring to coat the fennel with the oil. Season with salt and pepper and cook for an additional 5 minutes. Serve hot or at room temperature.