Is a benign cbd stricture considered as an obstruction to the bile duct? will it restrict the flow of bile unless treated?

Stricture means narrowing and narrowing causes restriction of flow. Whether you need treatment or not will depend on your symptoms and findings as determined by your doctor.

Yes, by definition, a stricture is a narrowing of the tube restricting at least partially flow. The need for treatment is dictated by the damage expressed in symptoms and or potential for causing complete obstruction.