Purely from a technical perspective and ignoring the political implications, I don't think that phones are helping all that much. I travel quite frequently and work with a lot of people across the US (as well as Europe and India), who also travel frequently.

I keep tab of who is - or might be - where on any given day, simply to be able to coordinate schedules and not call folks who are in PST at 6am by accident (or have people call me at 9pm).

A system for messengers (Skype, Slack, Teams, Text ...) where people could share their current time zone would make my life so much easier sometimes.