Heat the olive oil in a skillet over medium heat. Stir in the garlic and onion; cook and stir until the onion has softened and begun to brown slightly, about 7 minutes. Remove from heat and set aside.
Combine the vegetable broth, potatoes, carrots, corn, 1 1/2 cups soy milk, garlic powder salt, and pepper in a large pot. Bring to a boil over medium-high heat, then stir in the onion mixture. Reduce heat to medium-low and simmer, uncovered, until the potatoes and carrots are tender, about 20 minutes.
Whisk together the flour and remaining 1/2 cup soy milk in a bowl. Stir the mixture into the soup, and continue to simmer until the soup has thickened, about 10 minutes. Stir in the parsley before serving.
