The file reported in block code in the main issue is not valid neither for surefire neither for ant junitreport task (the main tools that generates a report JUnit).
In the sample there are too nested testsuite elements. Surefire report admit only one testsuite as root element. Ant junitreport task aggregates testsuite elements under a the root testsuites element. Skipped is a valid attribute for the testsuite element.
Is report generated directly by the PHPUnit tools?
If yes, please fill a bug to the PHP Unit tool, otherwise please post the original PHP reports that cause the issue so we can fix the XSLT that transform PHPUnit report to a valid JUnit report.