That's an old flip-phone, so unfortunately there won't be a way to sync those contacts with a Google account.
Does the phone have a SIM card? (If it was with Verizon or Sprint, then it probably doesn't.) If it has a SIM card, then see if you can export the contacts to the SIM card. If that's possible, then you might be able to swap that SIM card into the S6 and see if there's an Import from SIM option in the Contacts app.
Looks like it can send Vcards via Bluetooth, but the question is if it can successfully connect and communicate with a modern smartphone: https://www.manualslib.com/manual/630373/Lg-Vx8300.html?page=41