Phone calls have so much ceremony and ritual and take so much time to play phone tag, and every single part of that, especially the phone tag, has gotten so much worse because of spammers. Phone calls just don't feel reliable anymore. It's easier to assume you are more likely to hit someone's voicemail than reach them many hours of the day. It's easier to assume people don't even check their voicemail in some cases, because they expect a text message if it was important.
If it is an actual emergency, I need to know that they have received the communication in real time. I'm never leaving someone a voicemail in an emergency situation.
In an emergency, I can often text 15-20 people in the time it takes to try to get a phone call through to a single person. (Especially with the multiplying effects of copy and paste and group chats.) I'm still probably going to follow up with a bunch of people by phone calls after the texts go out, but most of that will be by request ("can you call me when you get a chance?" texts) for details or shared emotion bonding after the key points are already distributed (and possibly some emergency conditions better).