On more modern systems the posix functions have split out into the php-process package
Installed Packages
Name : php-process
Version : 7.2.24
Release : 1.module_el8.2.0+313+b04d0a66
Architecture : x86_64
Size : 100 k
Source : php-7.2.24-1.module_el8.2.0+313+b04d0a66.src.rpm
Repository : @System
From repo : appstream
Summary : Modules for PHP script using system process interfaces
URL : http://www.php.net/
License : PHP
Description : The php-process package contains dynamic shared objects which add
: support to PHP using system interfaces for inter-process
: communication.