I am creating a math app for a assitgnmen but the problem is that I need to conect my phone to see what it does but im not allowed to use my phone so i can't see what my code does.
They should fix this so you can test your code without using your phone.
So your teachers do not allow you to use your phone in class but want you to make an app?
Show them how App Inventor works and maybe they will change their mind. Let them join the community so we can convince them. 
You can, you can use the MIT supplied emulator, or a third party emulator such as Genymotion or Bluestacks. No Doubt your IT Department will need to get involved to allow for any of these.
Thank you
Or if you are using a recent chromebook, you can run the companion app as an app.
Our collection of emulators: