In order for the PhoneGap Build service to sign your app correctly “in the cloud” it needs both your Provisioning Profile and your Developer Profile. As long as you can run apps from Xcode on your devices you have them both.
For PhoneGap Build to utilise them you need to export them both via Keychain Access and then import them to the PhoneGap Build service. Once you’ve done that, PhoneGap Build can build iOS apps for you.
This article explains the procedure in detail: