The Phones of the New NATO Secretary General
electrospaces.net
electrospaces.net
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.