With the new version 3 of StarUML there wasn’t a UML to PHP Generator yet. I’ve decided to take the existing one for Java (https://github.com/staruml/staruml-java) and rewrote it so it would generate PHP code instead: https://github.com/nahakiole/staruml-php
I then submitted it to the StarUML extension Repository and to this date it has already been downloaded over 600 times.
If you find any bugs, report them to me and I’ll fix them as soon as possible.