CodePush allows you to send updates of application code like HTML/JS/CSS to your Apache Cordova app without having to resubmit to the App or Play Store. This is a huge benefit of hybrid apps where they don’t need to go through the app store review every time they need to tweak something.
PhoneGap Build allows you to build your entire app in the cloud. It does not provide a service to update your in production app. You would still need to go through app store approvals. You may be thinking of the Hydration functionality which is only available when your app is in dev.