Great question! Although I don’t know if there is a specific function for this on your particular phone, the best way to save the message is the simplest. Turn up the sound as high as you can and record it onto a digital recorder (like you would use for a lecture), a cassette recorder or your cell phone if you have a voice recorder on it. Then save it as an MP3 on to your computer for safe keeping. You can also Google your vtech model number to see if you can find an owner’s manual. They might have a way to save a recording in there. Probably not, but it’s worth a shot.
For more accessibility options, see Learn how to navigate Skype for Business using accessible features.

Apple repairs iPhones at the Genius Bar in Apple Stores and through their online mail-in repair service. Apple repairs are high-quality, but out-of-warranty repairs can be much more expensive than third-party solutions. If you're looking to save some money you're not covered by Apple's warranty, you may want to check out our other recommendations.
On Android, you have a couple of different options. If you don’t want to use Google Voice, you may want to check out the free version of any paid apps, as performance can vary from handset to handset.