can i undo a google contacts sync with an iphone

You can't

That's true, you can't "undo" this sync (I had the same problem - ended up with 524 email addresses on my Contacts list!). But after brainstorming with Eric P. at the Apple store (WA Square, Or), this is what we came up with. The good news is - it took me 20 mins, and I am back to "normal." So, give this a try (and never check the Google contacts again!).

I opened Address Book, created a new group & named it Contacts #1.

I clicked on All, and dragged the “cards” I wanted into Contacts#1. (I found that I could click,hold & scroll up through the names I wanted and drag more than one at a time.)

I exported the information to a folder of my “stuff” on thedesktop, just in case I lost anything.

I exited Address Book, plugged in my iPhone, selected Contacts #1 for the sync, held my breath while the phone did its thing, and viola! Done!

Hope this helps.