After experimenting with numerous small text editors, I found that nothing beats Visual Studio 2010 for source code editing. Yes, it is a bit large, but very capable. Most freeware and shareware was either buggy, had certain missing features or annoyances, or was too expensive.
So, I needed to simply add PHP syntax highlighting to Visual Studio 2010. While there is a shareware project called VS.PHP that looks pretty good, and may add syntax highlighting, I didn't want to pay $99 for it in 30 days. Searching further, I found the free, open source, offering Phalanger. While this actually has many more capabilities than simply adding PHP syntax highlighting to VS2010, I don't need those so won't get into them.
The bottom line is that if you work with PHP and VS2010, Phalanger is exactly what you need!