In a large saucepan over medium heat, saute celery and onion in butter until tender. Stir in flour until blended; gradually add milk. Bring to a boil; cook and stir for 2 minutes or until thickened.
Stir in the bouillon, cream, crab, mushrooms, basil, garlic powder, 1/4 teaspoon Creole seasoning and 1/8 teaspoon pepper. Bring to a boil. Reduce heat; cover and simmer for 20 minutes, stirring frequently. Season to taste with remaining Creole seasoning and pepper if desired.