How to visit php file in my custom directory under site root directory

Only Apache is “responsible for caring” that your script is PHP. AFAIK, whether you need to use AddHandler or AddType depends on whether your PHP is installed as a module or as CGI. You can try creating .htaccess in wp-mybiz/ folder containg some of the common solutions/workarounds

1) AddType application/x-httpd-php .php

2a) AddHandler application/x-httpd-php .php
2b) AddHandler x-httpd-php .php

or a combination of both.

To help isolate the real issue clear your cache and get the headers (i.e. via ‘Live HTTP Headers” or similar).

Edit: Excellent thread – https://www.webmasterworld.com/apache/4557229.htm