Prevent Voice Memos from ending up on iPhone when connecting to iTunes
You need to make sure that iTunes is not automatically syncing your iPhone when the latter is connected to your computer. In the iTunes Menu bar, go to iTunes → Preferences... and in the preferences window that opens click on the Devices tab. Now check Prevent iPods, iPhones and iPads from syncing automatically option.



Also, if you do have to sync your iPhone with your iTunes library, make sure Voice Memos are not selected.