I have built four .IPA packages using Phonegap Build in 2016 (four versions) of one published IOS app and submitted them successfully. Now with Phonegap Build ver 6.5.0 I get an Application Loader error: "You are not authorized to use this service for provider". Apple developer support sees no issues with my mobile provision certificate, distribution certificate or developer certificate. IS THERE A CHANGE IN PHONEGAP BUILD THAT EXPLAINS THE PROBLEM?
What version of the application loader are you using?
I am using the Application Loader under the Mac OS Xcode (ver 8.2.1) menu. I open Xcode then select Open Developer Tool > Application Loader. I am running on a big iMac using Mac OS X El Capitan Ver 10.11.6. During my successful 2016 experiences with PhoneGap Build and the Application Loader getting the App published and twice updated in the Apple IOS App Store, I used the same combination of PhoneGap Build and App Loader tools.
Did you ever find a resolution to your issue? I am experience the same thing.