Earlier quoted context omitted.
Where does it say this?
Section 1.3 of the Alexa Terms of Use: "...to provide and improve our services...". 1.3 Alexa Interactions. You control Alexa with your voice. Alexa streams audio to the cloud when you interact with Alexa. Alexa processes and retains your Alexa Interactions, such as your voice inputs, music playlists and your Alexa to-do and shopping lists, in the cloud to provide and improve our services. Learn more about these voic…
It's not very clear, though, and I feel like they could have made this clear very easily.
(I do expect Amazon to store the voiceprints of "Alexa, do foo" to improve their speech-to-text, as well as analyze the actual requests, yes, but I would hope that Amazon is not analyzing or storing the contents of calls.)