Not all security updates are worth downloading immediately, but Apple's iOS 12.2 contains a must-have.
Apple patched all of its operating systems yesterday (March 25), and one fix for iOS devices is incredibly important. The patch to the ReplayKit API fixes a flaw in how microphone data is handled -- and the flaw makes it possible for malicious apps to hear and record what's being said and done around your iPhone or iPad (or iPod Touch) without letting you know.
In a post explaining the update, Apple notes "An API issue existed in the handling of microphone data," and that the update solves the problem "with improved validation." iOS 12.2 also includes a protection to guard the Contacts app from malicious apps and to protect users from websites trying to "access sensor information" without user consent.
A patch to the WebKit rendering engine (which often gets updated in Apple's security patches) protects devices from malicious websites that could try to execute code on your phone and do what they want to your device.
How to update your iPhone
Open Settings, tap General, tap Software Update and tap Download and Install. Expect your phone to take a bit of time to reset, so don't do this while you're in the middle of something important.
Apple also issued other updates: macOS Mojave 10.14.4 (alongside Security Update 2019-002 for High Sierra and Sierra), Safari 12.1, tvOS 12.2, iTunes 12.9.4 for Windows and iCloud for Windows (v. 7.11).
The macOS patch provides similar user protections, including one that could lead to a malicious app getting kernel-level privileges, the most valuable and potentially dangerous set of system controls. From that point, those apps could do whatever they wanted to your Mac without your consent.