From the Cocoapods docs:
CocoaPods is built with Ruby and it will be installable with the default Ruby available on macOS.
AFAIK, it is meant for Xcode projects on Mac. Not for Windows.
Cocoapods is only required if you're embedding the webview (Embedding the Webview | PhoneGap Docs ) or include a plugin that requires cocoapods. This isn't something most PG apps have to worry about doing.
Note that if you plan on building locally, you do still need a Mac to build for iOS. But if you use PhoneGap Build for building, you can delay the need for a Mac until you need to publish to the app store. (And you can rent one to do that step, meaning you don't have to shell out a lot of cash.)