How Can I Acces Pocketmine Class Outside The Pocketmine App

depends on how you set it up and what
if you want data just have a plugin on your server to put needed data into a DB
on the webserver it should fetch it via DB
if you want to execute an action in server via webserver put the action to execute with paramaters into a DB table
the plugin on the server will periodically check for pendingactions DB table and execute as following, after execution it removes it from DB
this is probs one of many ways to get the same job done