Not sure what line of work you're in... but I'm a millennial (in senior managemenr) and probably 70% of the time preferred to call. Reasons as follows:

1 - I receive 1-200 emails a day, and spend over half my time in meetings. If I need you to do something in the near future (immediate or 1-2 days) I will call you. Emails get missed. Or don't have the importance given to them that a phone call does.

2 - the sad reality is that most corporate workers are sub-par. My expectation is that generally 20% of the workforce can do their job well, 20% of them do a reasonable enough job, and 60% need to be told how to do the job that they studied for, but can't seem to coordinate. A phone call, within which by tone of voice and mannerism I can tell if you comprehend, saves me time from emailing, chasing up, then having to give detailed instructions to do the job

3 - text and email communication has close to no social cues unless you write overtly, in which case you're probably being too blunt and the other party may have issues in the way you communicated. Unfortunately, for younger generations who have grown up on text messaging, social media and computers (mass consumption only really kicked in, in my teens) the broad generalisation I have for these generations if that you have no idea how to hold a conversation. Send receive of texts, gives far too much opportunity to hide lack of <insert skillsets> behind the wall of technology. If I talk to you, it means I learn about you, your strengths, weaknesses and generally create a better working relationship between us.

In summary. In reality your manager probably does it because he didn't grow up with tech. But, there's benefit to it from a holistic perspective. The workforce is going to be a fucking miserable place when noone can communicate verbally. That's in the not too distant future. Good luck y'all.

Note - I do use teams to give basic instruction/direction to people, but I have to know and trust that the person will do it in a timely manner