This function sends messages in BSD Syslog RFC 3164 format (https://tools.ietf.org/html/rfc3164).
To see the raw messages being sent by PHP to the logging socket, first stop your syslog/rsylsog/ng-syslog service, then listen to the logging socket with the netcat-openbsd package:
nc -U -l /dev/log
Now, log something from PHP:
<?php
syslog(LOG_LOCAL1|LOG_INFO, "Test from PHP");
?>
You will see the rfc3164 output from netcat:
<142>Oct 24 14:32:51 php: Test from PHP