You could pick up your phone and, uh, call the pizzeria, but that's so old school. Instead, use apps from Domino's, Pizza Hut, and Papa John's, to order your food. Using the apps should also help prevent mistakes on your order, since there's no chance they'll mishear your order.
The Domino's Pizza app lets you place an order for delivery or carry-out. You can select from its specialty pizzas or build your own. You can even order other items from the menu, like sandwiches, pasta, sides (wings), and desserts. When you get to checkout, you'll be provided an estimated wait time. You fill out your personal details then choose whether you're paying by cash or credit card. The most interesting part of the app is that it has a pizza tracker, to check where your order is in the delivery process. It goes from order placed, to prep, bake, quality check, then carry-out.
You can order from Pizza Hut's full menu with its app. You can choose from pizza, pasta, sides, desserts, and drinks. You can also peruse its specials to see if something catches your fancy. Though you don't need to sign up for an account, creating one will allow you to keep an order history so you can reorder your favorites.
The Papa John's app works pretty much the same way as the Pizza Hut app. You have full access to their menu, which includes pizza, sides, drinks and desserts. You can choose delivery or carry-out and place the order without an account. An account allows you to reorder favorites and participate in the Papa Rewards program.
That's it. In case you're wondering, Little Caesars does have an iPhone app, but disappointingly, it is just for locating stores and viewing the menu. Also keep in mind that the apps above are for ordering in the U.S. only.