I could see an argument for relaxing that for mobile voicemail, on the basis that mobile phones are pretty personal and not generally shared by multiple people, but I've no idea whether that may have happened. Or, indeed, whether such policies may vary between organisations within the NHS.
Website: https://www.stirruphope.org/storage/app/media/pdf-web-ready-disclaimers-email-twitter-facebook-voicemail.pdf

If you don’t know it by now, you might never know. Voicemail greetings are incredibly important to users. It conveys identity, character, and image to callers. In an increasingly digital world, where business is conducted online and over the phone, phone presence is increasingly important. As such, your greeting is a crucial part of the platform. While there are a number of obstacles to be aware of, utilized properly, voicemail greetings can be incredibly helpful and beneficial; therefore, its in users best interest to invest themselves in creating a quality recording.
It’s shocking to learn that 97% of calls go to voicemail but, after making hundreds of calls, most would agree the percentage feels at least that high. Consider the following before making a call: Where the lead came from Time of day the lead was received Keep your message short (under 20 seconds) Avoid giving away too much information Add information that will pique their interest Speak with confidence/authority Keep tone and delivery casual and friendly Be clear and concise