First make sure that you use the latest version of the phonegap widget and the cordova phonegap app If that's not the case then update them or re-Install them.
if the problem is not solved, please give the following a try!
Try different browsers maybe it is a browser compatibility problem.
I normally use Maxthon or the standard browser on my phone but those 2 doesn't work with mendix so I tried some browsers and finally I liked to use Firefox and Yandex. for my problem I use Firefox. Give it a try.
I didn't use the phonegap camera widget but another camera widget.
here a list of browsers I tried: