We should frame this story with what the actual end result of 'unlocking your phone' is when discussing it. The government routinely claims that it is no different than asking a traveler to open a physical briefcase. It is very different.
If you're treating the phone as a 'good' as indicated in the quotes on this story, you can inspect my phone as a good. You can look at the phone. You can xray it. You can open up the back cover to ensure it's a real battery inside and not something more sinister. All that would be fine and fall within what the law was intended for.
What the government is actually asking you to do is unlock your digital key to your entire digital identity for them to do with as they wish. Your phone has direct access to all your email accounts, all your personal and work files within the cloud (Dropbox, Box, iCloud, Google Drive, etc), your entire address book, your chat history, all your personal photos, your private PGP you use to sign communications to prove they came from you, etc, etc.
Asking to inspect your phone is fine. Asking to have complete access to your entire digital life, history, and identity is not. If I'm asked for the former, go ahead and inspect it, I put it through the scanner on every flight. If I'm asked for the latter, the answer will be no.