Hi Once you are done with your Application in App Builder. Under the Deployment Menu of App Builder, Select option Create Corodova Project which will generate Corodova project in your App Builder Workspace.
Second Step; got the project directory and zip www folder. Go to Adobe PhoneGap Build and upload your zip file. It will give you native binaries for all platforms. Download directly on your machine application binary or scan the QR code to download directly on your phone.
I have done it myself multiple times.If you face any problem let me know anytime.
Regards,
Mayur