Context does matter here. If the caller would reasonably expect you to answer the phone (such as if they were calling a store or other place of business), an apology for not being able to get to the phone makes the most sense.
Instead, your voice mail greeting, like everyone else’s, goes something like this:

05You have reached the offices of [your company/business]. Unfortunately, we are currently closed. We are usually open between [hours] [days] and closed on [days]. Please leave us a message with your details and we will get back to you when the office opens. You may hang up after leaving your message or press the [key] for other options. Thank you for your call. This after-hours voicemail greeting lets callers know how to do business or communicate with you outside normal business hours. You may also like 6 How to Ask for a Raise Email Templates to Get Your Point Across
In Australian English it’s pronounced with the vowel /a:/ like in ‘part’. Problems arise when people use the /ʌ/ vowel (like in ‘up’) instead of /æ/ or /a:/. If you do this is will sound like the worst swear word in English. Many non-native speakers often pronounce the vowel /æ/ more like /ʌ/ because they don’t have a vowel like /æ/ in their first language. Many speakers of European languages will do this (Spanish speakers and Italian speakers) and also speakers of Japanese and Korean. This problem with /æ/ also means that if you say the word ‘back’ in your voicemail greeting sample, you are likely to pronounce it more like ‘buck’. remember to pronounce word endings in English. Check you aren’t dropping any endings off or mispronouncing them.