View iPhone back up in iTunes
If you are just backing up your phone via wifi to your Mac there isn't a native tool to view the contacts.  (There are some third party tools, but I don't think that is what you need).  If you are syncing your iPhone to your Mac then they should show up in the contacts app.

More likely is that your contacts are being synced to whatever account you are using (gmail, yahoo, iCloud, etc...) and you just need to configure that account on your Mac and then you will see the contacts that way.