Hi,
I have over 20 years experience in programming with more than 15 years in web development and quite some years with mobile apps.
I am working with phonegap/cordova and I know how to get it back from the build APK file.
The remaining question is, if the code was obfuscated/minified/encrypted. Cause then it can also be converted back to a phongap project which can be rebuild, but you will not be able to understand the scripts.
So the best would be if you just send me the APK and I will have a look, if the code is readable. Like I said before, I can build you the phonegap project for sure, its just not possible for anyone to tell you if you will be able to understand the code if he/she does not have a look on its encryption.
I will be happy to hear from you soon.
Best regards,
Fabian