On macOS there is a tool called
fs_usage which can be used to see what files are accessed on the system while it is running. It needs sudo to run.
ps aux | grep php-fpm
sudo fs_usage -f "pathname" [pid]
accesschecks whether the calling process can access the file pathname
opencreates a new open file description, an entry in the system-wide table of open files
closecloses a file descriptor
stat64returns information about a file