There are hundreds of ways to secure a laptop and ensure your privacy. Why are there almost no good ways to use a smartphone in a secure and private way?

There's only one way to secure a laptop: use Qubes OS. It requires a lot of resources for the virtualization, and on the phone, it's not profitable for Apple and Google.

You can if you don't use a google certified rom, use primilarily a browser instead of apps and do not install the google play stuff.