LoadModule php4_module libexec/httpd/libphp4.soStepwise has a nice page of info on changes in 10.1 that covers this and other aspects of the upgrade; give it a visit to see some things to keep in mind as you upgrade.
AddModule mod_php4.c
AddType application/x-httpd-php .php
AddType application/x-httpd-php-source .phps

