Here is stated Apple policy taken directly from apple:
When you use Siri and Dictation the things you say and dictate will be recorded and sent to Apple to process your requests. Your device will also send Apple other information, such as your name and nickname; the names, nicknames, and relationship with you (e.g., “my dad”) of your address book contacts, song names in your collection, HomeKit-enabled devices in your home (e.g., “living room lights”), and the names of your photo albums (collectively, your “User Data”). All of this data is used to help Siri and Dictation on your iOS device and any paired Apple Watch understand you better and recognize what you say. It is not linked to other data that Apple may have from your use of other Apple services.
If you have Location Services turned on, the location of your device at the time you make a request will also be sent to Apple to help Siri and Dictation improve the accuracy of its response to your requests. You may choose to turn off Location Services for Siri. To do so, open Settings on your iOS device, tap Privacy, tap Location Services, tap Siri & Dictation and select “Never”.
You may choose to turn off Siri or Dictation at any time. To turn off Siri, open Settings on your iOS device, tap General, tap Siri, and slide the Siri switch to “off”. To turn off Dictation, open Settings, tap General, tap Keyboard, and slide the Enable Dictation switch to “off”. If you turn off both Siri and Dictation, Apple will delete your User Data, as well as your recent voice input data. Older voice input data that has been disassociated from you may be retained for a period of time to generally improve Siri, Dictation and dictation functionality in other Apple products and services. This voice input data may include audio files and transcripts of what you said, related diagnostic data, such as hardware and operating system specifications and performance statistics, and the approximate location of your device at the time the request was made.
You can also restrict the ability to use Siri & Dictation altogether under the Restrictions Setting.
By using Siri or Dictation, you agree and consent to Apple’s and its subsidiaries’ and agents’ transmission, collection, maintenance, processing, and use of this information, including your voice input and User Data, to provide and improve Siri, Dictation, and dictation functionality in other Apple products and services.
At all times, information collected by Apple will be treated in accordance with Apple’s Privacy Policy, which can be found at www.apple.com/privacy.
