Melt 3 tablespoons butter in a large skillet over medium heat, and add the canola oil. Stir in the celery and peppers; cook until tender, about 5 minutes. Add the green onions, hot sauce, and salt; cook and stir until onions are wilted, about 3 minutes. Stir the flour, shrimp, ricotta cheese, and milk into the pepper mixture; cook and stir until the shrimp turn pink, about 3 minutes. Remove from heat and cool.
Preheat oven to 425 degrees F (220 degrees C).
Melt 1/2 cup butter in a small saucepan over medium heat. Remove from heat and keep warm. Stack two sheets of phyllo on top of each other, and cut into 3 strips about 3 inches by 12 inches. Brush the top of each strip with melted butter, and place a teaspoon of the shrimp mixture at one end. Fold phyllo dough over the filling, working back and forth from side to side to make a triangle. Seal the end closed with a little water or butter. Place triangle on an ungreased baking sheet. Repeat with remaining phyllo sheets and filling.
Bake in preheated oven until tops are golden brown and flaky, 10 to 15 minutes. Cool on a wire rack.