Before any business can create clear, easy to hear (and understand) recorded audio messages, they need the right recording equipment. Many businesses try to get by with using audio recorded on a standard recording device.
Website: https://support.digium.com/community/s/article/How-do-I-record-my-Voicemail-Greeting-over-the-Phone

I have a confession to make: I haven’t recorded a new voicemail greeting since 2014. In the past four years, I (hopefully) have become more articulate, poised, and self-assured. But hear my voicemail recording, and you’d think I was still new to the work world, a little unsure of myself — and probably not an authority. Obviously I need toupdate it. And if you haven’t changed your voicemail greeting in over a year, you’re likely in the same boat. After all, a professional voicemail recording boosts your credibility, makes you seem more competent, and encourages whoever’s listening to it to continue the relationship. A relatively unprofessional one — like mine, for instance — does the opposite: It encourages prospects, recruiters, and potential connections to run in the other direction. With that in mind, I’ve written 18 unique voicemail greetings for every situation. Pick your favorite, practice a few times, then record your new voicemail.
What kind of company do you run? A law firm may prefer more formal business voicemail greetings than a trendy retail store, for example.