In Flash Builder, both FXP and FXPL are created the same. In the beta build, the three ways to achieve this are:
1. File > Export Flex Project (FXP)...
2. File > Export > Flash Builder Project...
3. Right click on project in package explorer, Export... > Flash Builder > Flash Builder Project
The only difference between an FXP and an FXPL is that an FXPL contains only a library project, whereas an FXP will always contain a Flex project and 0 or more library projects. When exporting a Flex project, library projects may be bundled with the FXP if the Flex project has dependencies on library projects in the workspace.
Engineer, Flash Builder