On inbound calls the phone will only ring once the jump to the next step in the call flow whether it is voicemail or another extension. This issue only happens on Monday, by Tuesday it has resolved itself somehow. This is defiantly a pattern as this is the 3rd Monday this has happened on. All 3 customers are running on Linux Debian 9.
There is a way to save a voice message on iOS mobile by recording it on Notes or Voice Memos and set them as voicemail greeting. Also, you can share them using SMS, Email, Airdrop, Google Drive, and more, to make a back-up of the recorded voicemail. It isn't delightful when you expect a client call and can't answer it at the moment. You can't get all your phone calls at all times, especially when you are busy with your work. That is why it is important to record voicemails on your iOS device and set it as a response on an incoming call. Therefore, we have listed the steps below on how to capture voicemails on iOS.

Forget about messing around with apps. There’s a powerful voicemail handling system built into nearly every big carrier today — and that system almost always includes a system for recording a voice message and sending it directly without ringing the target phone. I will walk you through the process of doing this on Straight Talk (since that happens to be my carrier) but most carriers will have similar systems.
When you first set up your Android phone, it may ask you to record your greeting for the caller. You can also keep the default greeting stored on the device. But, in future, if you want to customize the Voicemail greeting or want to create a new one, then you may need to delete the old recordings from Android. It may not be necessary depending on the Android device model & version; it’s good to know the process.