Here, the ophthalmologist is not in a position to receive a call. However, he/she makes sure the patient’s need is addressed.
On the Greeting page there are two options. The standard option is to use the default iPhone voicemail message, but you can also record a custom message. If you already have a custom iPhone voicemail message recorded, tap Play to listen to it now. Otherwise tap Custom.

But now I'm going to go ahead and record. So press record sorry I missed your call. Please leave your voicemail after the beep and I'll call you back. Thank you. Press stop and now. I could press play and then if I don't like what I hear, I could press record one more time and when I'm satisfied, I could press save on the top right and it's going to save my greeting and that's all I have to do to set a new voicemail on my iPhone. You could always come back to this page. Press record one more time and replace your voicemail here. You're greeting here, and you should always use someone else's phone to call to see how it sounds from a different device.
Here’s a simple clinician voicemail script if you want to keep your message to the point. Hello. You’ve reached Highland Family Counseling Services. We are currently unable to take your call, so please state your name, phone number, and a detailed message after the beep. We will return all calls within two business days.