What am I supposed to use then, an Android phone that openly sends to Google literally all data it can mine on me?
Nothing is safe from the internet/phone provider.
As for the phone itself, you can take Apple's word (lol), tweak the heck out of Android or use a custom Android ROM (beware rooting, it may limit what apps you can use).
The question about the Android ROM though is that there's no guarantee that's not compromised. Not only do you need to trust the person(s) creating the rom, Android allows closed source driver packs, kernel and bootloader to be used and so pretty much EVERYONE does this because investors HAAAAAATE open source (O.M.G. do they hate it!!!!). Not to mention going and installing Google apps on top of your install. Despite that sounding bad, and it is, you'd be surprised how much you can actually hide from Google and therefor everyone else.
While you have to take Apple's word for it, Google has ways to actually look at the data they have on file for you. Is it accurate? Hard to say, but it's still more than Apple's "trust me bro". I've used custom roms I built myself as well as various off the shelf ones with as much removed/disabled as possible and if you can trust what Google will show you, they didn't get much from me and based on the amount of spam and targeted ads I see it does seem to work.
Tips.
Remove Twatter/insta/faces etc, this is especially important if you use widgets. I do this before I even setup my account, just bypass setup.
If you cannot uninstall them, you can force disable them on newish Android, older versions need ADB and a computer to hack the phone (not as bad as it sounds).*
Go through all the Google specific settings on your phone to be as generic as possible.
Run Firefox Focus and Firefox with Ublock (yes on your phone), Firefox Forcus for quick stuff.
In network settings look for private dns and insert "dns.adguard.com" (no quotes)
Use fewer "free" apps and widgets, paid isn't always better though, pay attention to what it says before you try/buy.
There's also apps which can remove spying from your apps but that's a whole other topic.
*Beware what you disabel remove as it can cause the phone to crash. It's pretty safe these days but if you're concerned, search the app online and "safe to remove".
