Fundamentally un-American.
That being said, many countries across the world already do this to eliminate burner phones. And many messaging apps require a phone number anyways so this basically locks down anonymous messaging through a phone.
Free, anonymous political speech is the bedrock of American freedom. Also, guns
there still are a bunch of viable messaging apps/services that work without a phone number:
matrix, wire, deltachat, threema, maybe jabber/xmpp (depends on their support of encryption). any others?
> many messaging apps require a phone number
But not all, so what's the actual point?
Well - it's not exactly a surprise that all these non-American countries engage in un-American practices.
It's much more concerning when said practices are undertaken by the U.S.
Just because other countries do something isn't a justification to bring the practice into the U.S. despite that being a justification used with increasing prevalence these days.