Unfortunately, it's difficult to achieve a crispy texture when heating a frozen pizza in the microwave. Microwaves work by heating food using moisture, which can make the crust of the pizza soggy instead of crispy. However, if you're short on time and only have a microwave available, here are a few tips to improve the texture:
Use a microwave-safe crisping tray: Some microwave-safe crisping trays are designed to help make the bottom of foods crispier by elevating them and allowing hot air to circulate. These trays can help to some extent in achieving a slightly crisper crust.
Preheat the crisping tray: If you have a microwave-safe crisping tray, preheat it in the microwave for a minute or two before placing the pizza on it. This can help to start crisping the crust from the bottom.
Microwave in short bursts: Instead of microwaving the pizza continuously, try microwaving it in short bursts, such as 30 seconds at a time. This allows you to monitor the texture and prevent overcooking or drying out the pizza.
Finish with a quick broil: If your microwave has a broil function, you can try finishing the pizza by placing it under the broiler for a couple of minutes. This can help to brown and crisp the cheese on top.
While these tips may improve the texture slightly, they won't replicate the same level of crispiness you'd achieve with an oven. If possible, it's recommended to use a conventional oven or toaster oven to bake the frozen pizza according to the instructions on the packaging. This will yield the best results in terms of texture and flavor.