how do i make iphone sync all contacts from Google Contacts into IPhone?
I don't know how to get the phone to sync with a different group than My Contacts, or to sync all the contacts, but as long as you aren't using My Contacts for filing now, then you can have every contact in two groups - "My Contacts" for syncing and your chosen group for filing and organization.

You can do this without destroying the rest of your sorting scheme by selecting all contacts in each group in Google Contacts, opening the Groups menu, clicking the checkbox next to My Contacts until it shows up as a solid check mark (not a slash), and then clicking "apply" in the same menu. By selecting the checkbox instead of the name and using Apply, you are telling the UI to add them to My Contacts without moving them; this is a standard bit of Google UI style.