I'm having the same problem. Past week the build on Phonegap was fine. Maybe the AdmobAds plugins is not working anymore.
I'm getting this error on Phonegap log:
:compileArmv7ReleaseJavaWithJavac - is not incremental (e.g. outputs have changed, no previous execution, etc.).
/project/src/com/cranberrygame/cordova/plugin/ad/admob/AdMobOverlap.java:576: error: AdMobOverlap.MyRewardedVideoListener is not abstract and does not override abstract method onRewardedVideoCompleted() in RewardedVideoAdListener
class MyRewardedVideoListener implements RewardedVideoAdListener {