The most secure smartphones are Android smartphones. Don't buy that? Apple's latest version of iOS 11 was cracked a day -- a day! -- after it was released.
So Android is perfect? Heck no!
Android is under constant attack and older versions are far more vulnerable than new ones. Way too many smartphone vendors still don't issue Google's monthly Android security patches in a timely fashion, or at all. And, zero-day attacks still pop up.
So, what can you do to protect yourself? A lot actually.