Phonegap and cordova uses almost the same repository,but they are not the same.Phonegap is build on top of cordova.
Cordova's releases a version first and phonegap usually follows.
The main difference between the both is that phonegap allows you to build your app online https://build.phonegap.com/
Both have very different documentation
Here's a link to cordova http://cordova.apache.org/docs/en/3.0.0/guide_cli_index.md.html
And link to phonegap http://docs.phonegap.com/en/3.0.0/guide_cli_index.md.html
If you notice the links in the phonegap plugin in the documentary,you will notice phonegap uses cordova's plugin
Phonegap constantly plays catch up with cordova.I am a little biased towards cordova.I suggest you decide which is better for you