Have a look at this question and this question.
Here's a sample .htaccess file that can handle PHP scripts without the trailing .php extension:
RewriteEngine on
#unless directory, remove trailing slash
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)/$ $1 [R=301,L]
#redirect external .php requests to extensionless url
RewriteCond %{THE_REQUEST} ^(.*)\.php([#?][^\ ]*)?\ HTTP/
RewriteRule ^(.*)\.php$ $1 [R=301,L]
#resolve .php file for extensionless php urls
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}\.php -f
RewriteRule ^(.*)$ $1.php [L]