Outlook Web Access [OWA] is a web interface that communicates directly with the Exchange Server. It is a real-time link with the Exchange Server. For this reason, there is no way to create or view existing Personal Folders within OWA. Personal Folders [.PST] are specific to a local computer; they are not created or stored on the Exchange Server.
If you wish to create and use Personal Folders, you will have to use a desktop version of Outlook.