Based on the information provided in the knowledge sources, I can address your question about the error you encountered when trying to register a new account with an existing phone number in Ory Kratos. The error message "An account with the same identifier (email, phone, username, ...) exists already." is a standard response from Ory Kratos when attempting to register with an identifier that is already in use [Docs > Kratos > Concepts > ui-messages](https://www.ory.sh/docs/kratos/concepts/ui-messages#an-account-with-the-same-identifier-email-phone-username--exists-already-4000007). This behavior is by design to ensure uniqueness of identifiers across accounts. Unfortunately, there is no direct way to make phone numbers non-unique in Ory Kratos. The system is designed to use identifiers (including phone numbers) as unique keys for accounts. This is a fundamental aspect of how Ory Kratos manages identities and cannot be easily changed without potentially compromising the security and integrity of the authentication system. As mentioned in the [Docs > Kratos > Manage-identities > Customize identity schemas](https://www.ory.sh/docs/kratos/manage-identities/customize-identity-schema#phone-number) section, when a phone number is marked as an identifier in the identity schema, it allows users to log in with that phone number. However, this also means that the phone number must be unique across all accounts. If your use case absolutely requires non-unique phone numbers, you might need to consider alternative approaches or custom solutions outside of Ory Kratos' standard functionality. However, this would likely involve significant modifications to the core behavior of the system and is not recommended. It's important to note that allowing non-unique identifiers could lead to security issues and complications in user management. If you have a specific use case that requires this, it might be worth reconsidering your authentication strategy or consulting with Ory's support team for potential workarounds that maintain the security of your system.