Add tomatoes, celery, carrots, chicken broth, onions, oregano, basil, and bay leaf to the pressure cooker. Cook on high for 15 minutes.
While the soup cooks place your butter and flour in a skillet over low heat. Constantly stir with a whisk for 5-7 minutes. Slowly stir in 1 cup hot soup. Add another 3 cups and stir until smooth. Add all back to the slow cooker. Remove the bay leaf.
Blend the soup with your blender or Immersion blender until smooth.
Stir in your cheese, milk, salt, and pepper.