I attempted this. I'm sure it's not water tight but it was successful at preventing me from giving away my usage data too easily.
In brief:
- a custom android ROM and NO gapps
- no Google play services
- f droid for apps
- yalp store (from f droid) for must have play store apps (although support is questionable)
- I took a new email from proton mail
- OSM for maps. SUCKS but a good alternative. Can't complain.
- dickduckgo privacy browser
- then just avoid the big tech companies (google, Facebook, Amazon, etc)
Cons: a much less streamlined experience.
Pros: some peace of mind about data.
Because the phone is more basic, you don't want to fiddle with it as much. Enjoy life!