Click on the Contact Type dropdown and select your gmail account from the list. The default is to add to Phone so that won't synch to gmail.
To add a gmail contact to an existing phone contact, edit it and then select New contact from the menu and select gmail for it's type. Copy and paste the info from teh phone contact and then it will synch to google.
You can separate the two and delete the phone entry later if you want, otherwise they will stay joined on the phone.