FTA:
"The red labels on this phone indicate that it is used for secure calls. As this phone has no encryption capability itself, it is connected to a dedicated Voice over IP network with bulk network encryptors that encrypt the outgoing and decrypt the incoming traffic."It also says, of the same phone (Cisco 8865), that "a similar model, for example, is in the Oval Office on the desk of the President of the United States".
Of course it's possible that the user whose comment you replied to has a better understanding of opsec than both NATO and US 3 letter agencies, but I strongly suspect they're vary aware of the security related to their Cisco products and are either confident that they're secure, or they only use them for non-confidential conversations and have a separate secure line for anything important.