https://www.php.net/license/

according to release 8.6 the license will be under 3 clause bsd which means you can combine it with vulkan webapis

Also this retroactively opens up past PHP versions.

" 5. The PHP Group may publish revised and/or new versions of the
license from time to time. Each version will be given a
distinguishing version number.
Once covered code has been published under a particular version
of the license, you may always continue to use it under the terms
of that version. You may also choose to use such covered code
under the terms of any subsequent version of the license
published by the PHP Group. No one other than the PHP Group has
the right to modify the terms applicable to covered code created
under this License."

So technically 8.5 you can use under PHP license version 4