Welcome to Android Central! It depends on which account the contacts on your previous phone were saved to. If they were saved to your Google account (which is what I strongly recommend), they sync automatically to your Google Contacts in the cloud, and are therefore safe if anything happens to the phone. If they were saved to the local Phone account, and you didn't back them up manually (they don't sync automatically anywhere), then they're gone.
You can tell which account a contact is saved to by bringing up the details of the contact--it should be listed there. When you're entering a new contact, it's one of the first things you can choose in the entry fields.