How can I make my smartphone more secure?

Question

I am become increasingly concerned about my privacy. I would like to make my smartphone more secure, less prone to attacks, become less reliant on big apps run by companies with questionable morals and send less data to Google and/or the manufacturer. Any tips would be of great help. Thank you.

seanw444 · Accepted Answer

For Android phones, I hear GrapheneOS and CalyxOS are great custom ROMs that can significantly improve privacy.
For any phone, the only VPN I really trust lately is Mullvad. Pay with mailed cash, crypto, or (if you really have to) a credit card or PayPal. With harder-to-trace payment methods, and the fact that they only give you a random account number (no email, phone number, address, name, etc. attached to your account) makes it the best at its job of any that I've seen. A VPN only improves your privacy if the VPN provider itself is trustworthy and proven.
Oh, and don't use the built-in browser if you're on Android. iOS as well, but to a lesser extent. Apple is pretty good about privacy when it comes to not leaking your stuff to other companies, but that doesn't mean Apple isn't spying on you. I've been running a hardened Firefox mobile for some time, but that's a deeper topic on its own.
You can find great privacy-respecting, free and open source apps on the F-Droid repository for Android too. Take a peak around there and see if you find some software that can replace your daily drivers.