If the contacts are saved to your phone's internal memory (or other service available to your Contacts app), you should be able to Move contacts to Google from the Contacts App's settings. I'm on a Samsung S8 so not sure if the process is the same (but the functionality IS definitely there, just might be called something different). On this phone it's under MANAGE CONTACTS, and then MOVE CONTACTS FROM PHONE. Select your Google account, and done.
You can also manually export your contacts to a file and then import them from Google, but that's the 'manual' way.