Phonegap Build with cli-9.0.0 uses cordova-ios 5.0.1, as far as I remember, cordova-ios 5.0.1 supports iOS 9+.
The App Store doesn't have a min, what the App Store requires is to use SDK 13 to compile, to do that you have to use Xcode 11, which Phonegap Build servers don't use yet, so at the moment you can't submit apps created from Phonegap Build.