CSE HTML Validator Standard and above can integrate with PHP's syntax checker for easy PHP script syntax checking. Simply download & install PHP and then point CSE HTML Validator to it.
You can also use CSE HTML Validator to check the HTML output of your PHP scripts.
c:\PHP or C:\Program Files\PHP\php.exe. Either the "thread safe" or "non thread safe" download options should work.php.exe is set correctly to something like C:\PHP\php.exe.F6 to check it. The results should appear in the Results Window at the bottom of the window.
The validation results, which include the PHP syntax check, are shown at the bottom of the window in the Results Window. Notice the PHP syntax error for the double right parenthesis in the echo() function. Validator messages from the PHP syntax checker begin with "[PHP]".

The PHP Checker options page in the Validator Engine Options of CSE HTML Validator.