Place all of the dried mushrooms in a bowl or large measuring cup and cover with about 1 cup of hot water. Let the mushrooms sit and soften for about 15 minutes.
Heat the oil in a stockpot over medium-high heat, and add the Baby Bella mushrooms, carrots, celery, onions, and garlic. Saute the vegetables for about 10 minutes, or until they start to wilt and turn lightly golden. Reduce the heat to medium-low.
When the dried mushrooms are softened, remove them from the liquid, reserving the mushroom liquid, and put the mushrooms in a colander. Rinse the mushrooms well to remove any sand or grit.
Mince the softened dried mushrooms and add them to the vegetables in the stockpot.
Drain the mushroom stock through a coffee filter or cheesecloth and add it to the stockpot. Add the chicken stock as well.
Turn the heat to high, and bring the soup to a boil.
Add the barley, and let the soup return to a boil. Add the dried thyme, and salt to taste. Reduce the heat to low, cover the soup, and let it simmer for about an hour, or until the barley is tender.
Add the minced sage just before serving. Taste and adjust any seasonings.