Phone-only contacts don't get synced to Google, only Google contacts do, so you need to create them in the right contacts list in the first place. I don't know of a way to convert them across, however if you look on Google Marketplace I think there are apps to export contacts, look for one that can export them to VCF format then you can log into gmail and import them, then they will sync back down to the phone and you can then delete the phone-only versions. If the contacts export programme exports your contacts as individual VCFs, I found that concatenating them all together into one file still worked with gmail's contacts import.