.htaccess rules doesn’t work for .php files but for .html works

Question

My very simple .htaccess rules doesn’t work for .php files but for .html works fine.

RewriteEngine On
RewriteRule ^about$ about.html [NC]

This one correct display about.html when i user /about

RewriteEngine On
RewriteRule ^about$ about.php [NC]

This doesn’t work. Do you have any idea? Ubuntu 16 server with apache2

And one more, when i remove

RewriteRule ^about$ about.html [NC]

from first options redirection still works…

My conf looks like this:

<Directory /var/www/html>
    Options Indexes FollowSymLinks MultiViews
    AllowOverride all
    Order allow,deny
    allow from all
</Directory>