the best (Windows) software i have found to do PHP and UML is Sparx Systems Enterprise Architect. besides a pletora of features, it supports the following for PHP:
- Reverse engineer object oriented PHP into UML class diagrams
- Generate PHP class definitions from UML class diagrams
- Synchronize changes made in a UML class into the corresponding PHP class definition
- Synchronize changes made in a PHP class definition into the corresponding UML class
- Create UML sequence diagrams to show what PHP classes use and how they are used
- Produce detailed documentation of your PHP code in standard RTF and HTML format
- Perform code engineering on models to generate base PHP pages.
not free ($199), but definitely worth the money.