Phonon asset validation is not a part of the protocol, but we felt inclined to include it in the documentation as it becomes an instrumental element in the trust and use of the protocol.
Phonon asset validation becomes a step in the process of managing phonons. Tools and applications created with the protocol could including an asset validation step that can confirm the validity of the asset on a blockchain. For example, when receiving a transfer request, an application could validate the asset and allow the end user to determine whether to accept the transfer or not.
Remember, phonon is a protocol to securely hold and transfer a private key. Phonon doesn't care what that private key is for, it's up to the applications using the protocol to determine what the private key represents is valid.
With that in mind, the team has developed asset validation tools for developers to include in their applications.