The idea is that every 15 minutes you create a new byte string and start spreading that. This makes it impossible to track who is seeing who or who is going where over longer periods. That is, unless someone releases their own key, which makes it possible to derive all the strings they would have spread.

This is not obfuscation or hand waving. You are not actually identifiable unless you choose to be.

Then again, if you want to avoid giving data to Apple and Google I would advise against a smartphone. I don’t think there is a way to use them that would satisfy your requirements.