Open the Messages app on your iPhone
Find the conversation with the voice message
Press and hold the voice message
Tap Save or Keep
Connect your iPhone to your computer with a USB cable
Open Finder on Mac or iTunes on Windows
Back up your iPhone to the computer
Use a backup extractor tool to access the saved voice message from the backup
Alternatively, open the conversation on a Mac signed in with the same Apple ID and save the audio file if available
Use AirDrop to send the voice message to a Mac
Use email or Files to export the voice message if the option appears
Upload the voice message to iCloud Drive and download it on your computer
Use a third-party transfer app to copy the voice message from iPhone to computer