The Smartphones producer commented that private keys should be stored offline to maximize their security, which means that they should not reside on a mobile phone or any device that connects to the internet regularly.
The blog post comments that mobile phone cryptocurrency wallets are the best place to store "spendable" money due to the phone feature called Trusted Execution Environment (TEE).
Good advices. If you put spendable in the subject title as well, it would not be controversial anymore (but at least I can confirm you have skills how to create click-bait titles)