This work for me, to redirect logs to a separate syslog file
put this line in your /etc/syslog.conf :
local0.debug /var/log/php.log
Then restart syslogd:
/etc/init.d/syslog restart
php example:
<?php
define_syslog_variables();
openlog("TextLog", LOG_PID, LOG_LOCAL0);
$data = date("Y/m/d H:i:s");
syslog(LOG_DEBUG,"Messagge: $data");
closelog();
?>