everyone's ID is tied to their smartphone
Intesting theory, but lacks security. Everyone knows that data is shared these days, so my identity could technically be on more than one cell phone. This is especially true since my cell phone is shared with other people, it could have more than one person's identity.
Now the real question. Who is going to stop someone else from using my digital identity? The answer to that might surprise you, because I am the person that is going to stop them from using my identity. The government or companies do not care if it matches the individual, just that it is valid.