Is it possible to get back one earlier "copy" to paste it back? I typed for 200 words to send to a customer support of a company, and then I copied the content just to keep a copy in my Gmail or Google Docs.
However, before I pasted, I made a phone call using Google voice and pasted the phone number to Google Voice call to dial the number.
So the 200 words content is gone.  Is there a way to get it back?  The 200 words is such a small size (probably less than 2kbyte), and this MacBook is used only by me, so I don't worry about privacy of being able to show earlier copy and paste contents.  Is there a way to get that earlier copy back?
Not by default, no. The pasteboard is a temporary storage area, with no safety net. (One of the reasons that MacOS didn't have Cut and Paste of files in the Finder for many years, it is often said.)
There are plenty of apps in the Mac App Store, and elsewhere, that enhance the Pasteboard's capabilities by storing the pasteboard's 'history'.
I use Yoink, which does many Drag-Copy-Paste things, including this. Other more simple apps include things like CommandClip, which just keeps the last 10 text entries. Note that this may include passwords, so care should be taken.