There is a handy utility called Directory Utility which allows you to configure connections to directory servers. It also contains information for persistent NFS mounts across reboots. If you ever wondered where these phantom mounts came from or you are trying to eliminate a mount that no longer exists go to /System/Library/CoreServices/Directory Utility.
From within Directory utility, click on Directory Editor and then select Mounts from the Viewing categories. There you will find all mounts and add/remove as required.