Import/Export
You could try the Import/Export to SD card feature.
1. Open the People app.
2. Hit the menu button and choose "Import/Export".
3. Select "Export to SD card".
4. Choose the "Phone" account to export.
5. The Evo will then create a vCard file (.vcf format) of all your contacts in the "Phone" account and store it on the SD card.
Now for the tricky part. You'll need to get rid of all the contacts in the "Phone" account. Otherwise, when you import them back in from the SD card, you'll have duplicates that will automatically link to the Google contacts.
1. Hit the menu button and choose "View".
2. Uncheck everything except "Phone", then hit "Done". This will make the phone only show the contacts in the "Phone" account.
3. Hit menu, then choose "Delete".
4. Hit menu again, then choose "Select All".
5. Choose "Delete (x)" ...where (x) is the number of contacts you have in the "Phone" account.
6. Now change your view again so that it shows all your contact accounts: Menu|View... Re-check the appropriate accounts.
Now you will want to import the contacts into your Google account.
1. Hit menu and choose "Import/Export".
2. Choose "Import from SD card".
3. Choose "Google" for the account that the imported contacts will be created in.
4. The phone will search for the vCard file and import the contacts into your Google account. (Give this some time... It will take a while before the contacts sync to the cloud and show up on the phone.)
Hope this helps.
P.S. I don't know if there is an app out there that does this automatically, but in case there isn't, this should fix you up.
P.S.S. The next time you create a contact with your phone, be sure to choose "Google" as the account type. Then, from that point forward it should default to Google when you create subsequent contacts.