$_SERVER['PATH_INFO'] will return /99. You could then use trim() or substr() to remove the /.
'PATH_INFO'
Contains any client-provided pathname information trailing the actual script
filename but preceding the query string, if available. For instance, if the
current script was accessed via the URL
http://www.example.com/php/path_info.php/some/stuff?foo=bar, then
$_SERVER['PATH_INFO'] would contain /some/stuff.
from http://php.net/manual/en/reserved.variables.server.php
Update
Based on your comment, I'm a bit confused on what you are attempting exactly. If you are getting [object Object] back that means that you tried to send a JavaScript object as part of the URI. I would suggest using the HTTP Request body for any json data. If you intend to use the URI to uniquely identify the data you are sending to the server (like '99'), then the code above will help you to parse the URI. If you are wondering how to parse an HTTP request payload, then the following code will help.
Example POST request using json from the command line:
curl -i -X POST -d '{"a": 1, "b": "abc"}' http://localhost:8080/test/rdp3.php/99
Using PHP to parse the json object:
<?php
$data = json_decode(file_get_contents("php://input"));
var_dump($data); // $data is of type stdClass so it can be treated like an object.
var_dump($data->a); // => 1
var_dump($data->b); // => abcd
urlencode(), and will output[Object object]