It's red flag behavior, and often passive aggressive.
There's rarely a good reason to use voice notes. People should be doing voice to text in 99.9% of cases where they do just voice.
Discussion
I've noticed the trend spreading quite rapidly - many voicenotes back and forth instead of a call.
It's not always in the context of an argument either, sometimes it's a quick catch-up or something like that.
Are phonecalls just not in vogue or something?