When you invoke Phing and configure a custom build script, the working directory of Phing is set to the same directory where your custom build script is located in. This makes it difficult to run Phing from your local development environment and Jenkins.
I currently have to set the basedir setting of my project to "../../" instead of "." because my build script is located in "Build/Phing" (relative to the root directory of my project). For a developer it would be more logical that a Phing job runs successfully if you execute it from the root of your project, e.g. "phing -f Build/Phing/Master.xml".
In my situation the Phing plugin in Jenkins invokes Phing from the "<workspace>/Build/Phing" directory. This means that a developer first has to change to this directory when he wants to execute the Phing build locally. I would like to suggest that Jenkins executes Phing the same way as you would normally in your local environment.
This problem can be circumvented by simply using a execute shell build step which invokes phing using the following command (in my example) "phing -f Build/Phing/Master.xml <target>" but I prefer to keep using the Phing plugin of Jenkins if it would work correctly.