Well, in my case...I ported my phone book over from my previous phone via the Verizon backup assistant. The Droid X also syncs my Gmail contacts.
In some instances, I would have a VZ phone book entry for someone, and a Gmail contact entry for the same person. Just named different. Like on the phone I may just display their first name (eg: Bob) and only have their phone number but my Gmail contacts would display their full name (eg: Bob Jones) and have just their email address. Linking the two together eliminates redundant entries and puts all their info into one handy contact.
The linked profiles shows where the phone is getting the information from for that contact. If you entered it into the phone, it will just show as "Phone Contacts." If it's pulled from your Gmail, it'll show "Gmail." If you did like I did above, then it would show both.
If I continue to allow contacts to be linked, many don't show the contacts' phone #s. If I unlink them, then they show the phone #s in the phone contact. I even tried to unlink them, verified the phone #s were visible (they were), & then relinked them hoping it was just a glitch in the system with an easy fix, but no, the phone #s don't show when re-linked. It's as if the Facebook entry has overridden the rest of the contact's information. Do I really have to unlink all of my Facebook contacts (all of which came automatically over to my phone when the Verizon store transferred all of my contacts, etc.) in order to view phone #s? If so, I may have to rename many of my unlinked contacts so that "(Facebook)" or "(phone info)" shows in the new, unlinked name.