This is optional, but you can also leave another form of contact on your voicemail, like an email, that the employer who is calling can utilize. This will show that you want to get back to them as quickly as possible, and you are giving them multiple ways to do so. This isn’t necessary, but can be a good step if you want to squeeze a little more into the voicemail without going overboard.
If you persistently can’t save your greeting, you may need to reset your phone’s network settings. The iPhone needs to access your network’s data connection to save changes to your voice mail configuration, and if it can’t connect to 3G or 4G, it won’t save the changes. Start the Google Voice app. Tap the three horizontal lines at the top left of the screen (sometimes called a hamburger menu), and then tap “Settings.” In the Voicemail section, tap “Voicemail greeting.” Tap “Record a greeting.” How do I access my voicemail? To call your voicemail on an Android phone, simply open your phone’s dial pad and hold your finger down on the “1” key. You can also call your voicemail from a different phone by calling your own number and tapping the pound key. How do you check your voicemail?

Website: https://support.digium.com/community/s/article/How-do-I-record-my-Voicemail-Greeting-over-the-Phone
Calmly and steadily record your voicemail. Don’t rush it to the point where the customer can’t decipher everything you’ve requested on the message. To ease the process, write your voicemail down with pause points. This will ensure you annunciate everything clearly and can assist in managing your speed.