Melt butter in an Instant Pot set to SautÃ©. Add celery, carrots, onion and garlic; cook until soft and fragrant, 5 to 8 minutes. Sprinkle 2 tablespoons flour over vegetables, stir and cook 1 minute.
Add chicken stock, chicken breast, sage, bay leaves and pepper. Cover and cook on high pressure 20 minutes. Release pressure with quick or natural release. Remove chicken; shred or chop. Discard bay leaves; return chicken to pot. Add egg noodles and season with salt and pepper to tase.