Keep Audio Messages Forever In iOS 11

In iOS 11 devices, by default the audio messages are configured to be automatically deleted 2 minutes after you send them or have listened to the ones you received.
Even though this behavior helps you use your device’s and iCloud’s storage optimally, the automated removal may also erase the audio messages that may be important to maintain some official records and/or documentations.
That said, if you wish to keep all the audio messages forever in your storage so that you can remove the unwanted ones manually, the process is simple. Here’s how:
    Get to the Settings window
    Tap Settings from the Home screen. This opens the Settings window that lets you configure and customize your iDevice’s settings to best suit your preferences.

    Get to the message settings window
    Scroll down and tap Messages. This opens the Messages window. This window contains all the setting options that you can configure to make the app function as needed.

    Keep audio messages forever

Tap Expire from under the AUDIO MESSAGES section, and tap Never on the Expire window. This prevents the audio messages from being deleted automatically, and keeps them forever until they are removed manually.