Is there a way to search my Samsung SCH-R500 phone through a Terminal window?
There's probably not much you can do. I had an old Sony Ericsson phone which I could connect to with Bluetooth File Exchange; it allowed me to copy ringtone files back and forth but that's about it.

Older, "non-smart" phones aren't full computers in the same way that iPhone or Android phones are. When you use Bluetooth File Exchange the device is providing limited access to some data that it decides to export; you aren't interacting with the files directly. So even if you could access it via the Terminal, you wouldn't see a file system with files you could copy to your Mac.

If you're trying to recover specific data from your phone, like ringtones or address book info, you're better off asking a question about that ("How do I copy ringtones from my Samsung XYZ phone?"), and giving as much info about your phone (model number, version numbers on any info screens) as possible.