Demand for phones at Amazon is 5,000 per month. The holding cost at Amazon is 25 percent and the company incurs a fixed cost of $500 for each order placed. The supplier offers a marginal unit quantity discount with a price of $200 per phone for the first 10,000 phones in an order, a price of $195 for the next 10,000 phones in the order, and a price of $190 for the quantity above 20,000 in the order. How many phones should Amazon order per replenishment?