To successfully create UML diagrams with phUML you will need to install the graphviz toolkit.
phUML will use either
dot commands to create class diagrams.
How does it look like?
The image shown here, is the class diagram generated by phUML when it's executed against its original codebase. This image is hardly readable, because it has been resized to fit in the layout of this page. You can take a look at the complete image by clicking here.