Cover the clams with cold water and use a stiff brush to scrub the shells; discard any clams that are open and won’t close when thumped against another clam. Lift the clams out of the water, discard the water and repeat washing two or three times, until no sand remains in the water.
Heat the oil in a large (5-quart) pot over medium-low heat. Add the minced garlic, red chile flakes, and fennel and cook, stirring often, until the garlic is translucent, about 5 minutes. Increase the heat to medium; add the sausage and cook until the outside is no longer pink, about 2 minutes. Increase the heat to medium high, pour in the wine, and boil until it has reduced to about 3 Tbs., about 7 minutes. Stir in the marinara and bring to a quick boil. Put the clams in the pan, cover, and cook until they’ve opened, about 5 minutes; check often to avoid overcooking.
Meanwhile, toast the bread. Rub each toasted slice with the cut side of the garlic clove and brush with olive oil.
Serve the clams in wide bowls with the parsley sprinkled on top and the toast tucked into the sides.