“What Happens on your iPhone, Stays on your iPhone” - they said
Edit: Yes, this is confirmed in Apple's privacy policy for location services.
"If Location Services is on, your iPhone will periodically send the geo-tagged locations of nearby Wi-Fi hotspots and cell towers (where supported by a device) in an anonymous and encrypted form to Apple, to be used for augmenting this crowd-sourced database of Wi-Fi hotspot and cell tower locations."
Unless you tell your iPhone to send everything you have to Amazon, or Dropbox, or iCloud, or Google, or Facebook, or Backblaze, or [insert cloud service subject to Chinese, EU, or US law here].
[0] https://www.reddit.com/r/backblaze/comments/mncrsn/-/gu0dvf7...