There are a few different ways to control your mouse with your phone. One way is to download a remote desktop app like Microsoft Remote Desktop or Splashtop. With these apps, you can control your mouse and keyboard from your phone.
Another way to control your mouse with your phone is to use a Bluetooth mouse. Most Bluetooth mice come with a USB dongle that you can plug into your computer. Once your mouse is paired with your phone, you should be able to use it just like a regular mouse.
If you don't want to use a remote desktop app or a Bluetooth mouse, you can also try using your phone's touchscreen. Many phones have a built-in feature that lets you use your phone's touchscreen as a trackpad. To enable this feature, go to your phone's settings and look for the "touchscreen" or "display" settings.