We underestimate the bandwidth of a phone call. We can speak faster than we can type. We can listen to a big block of text more comfortably than we can read it. And that doesn't take into account the annotations about the rhythm, pitch, tone, etc. Face-to-face bandwidth is even higher, but not that much higher. Phone calls convey 80% of the information with 2% the effort.

Still, text messages (SMS or Slack or what have you) are even more convenient. So I would say it depends on the question. A question like, "What is wrong with the syntax in this line of code," is far better by text. But a question like, "How do you suggest we reconcile these two contradictory requests from our customers," might take less time over phone.

The rule I'm trying follow is this: If a reply to one of my emails suggests disagreement or misunderstanding, I usually try to catch them on the phone, rather than trying to clear things up with another reply. My experience is that these emails take several replies to clear things up, and sometimes there is a damage to rapport. A friendly phone call keeps rapport at the same level or even adds health points.