Here's how. I'll even show you how to remove all voice memos from your iPhone without using the ridiculously hard-to-use iTunes software.
Solution
Please watch this video to see how to delete all iPhone voice memos permanently.
Simply delete the voice memo one by one on your iPhone. It takes time, but the times it takes is far less than the time it takes you to find a solution online only to find that it doesn't work later.
I know it sucks, but if you can delete one voice memo within one second, you can delete 60 in one minute, or 600 in ten minutes. Ten minutes is nothing compared to what you will be spending online searching for a solution that doesn't exist at the time of the writing.
Questions?