You will need to open the XCode project that is generated for you when you executed the build
command and generate the IPA from there using Archive...
from the Product
menu. In reality though it’s not as simple as that, you’ll need to set up certificates and provisioning profiles first.
Here’s a good place to start: http://cordova.apache.org/docs/en/3.3.0/guide_platforms_ios_index.md.html