RewriteEngine On

# Redirect requests for .php files (as before)
RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /([^.]+)\.php [NC]
RewriteRule ^ /%1 [L,R=301]

# Internally rewrite requests WITHOUT .php to the actual .php file (explicit)
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_URI}.php -f
RewriteRule ^(.*)$ $1.php [L]