I have an older PHP project on a customer server, with no access to the config files, the server is runner nginx, and PHP 5.4 ...
Is there a way to use Silex Framework or another modern PHP framework from a subfolder? .. e-g. example.com/silexproject/ without access the .config file for the webserver?
is there an nginx alternativ to .htaccess ?
A quick google serach, shows that no, there is not an .htaccess like file for nginx. Quoting the official wiki:
Stop using .htaccess. It's horrible for performance. Nginx is designed to be efficient. Adding something like this would destroy that.
Keep in mind that you can still use Silex (I imagine that you can use any modern PHP framework as well) you just need to remember to call the front controller every time (so your URLs won't be that pretty).
For example if your project is on http://example.com/projectdir/ your front controller most likely will be http://example.com/projectdir/index.php and if you need to access some resource under that path, you'll need to type http://example.com/projectdir/index.php/path/to/resource (notice the name of the front controller in the URL)
My advice is that you'll try to contact whomever has access to nginx config file and ask if they can change the nginx config.