Despite this, “best” does not mean “impregnable”. The FBI claims that iPhones are “bricks” containing no useful information and Apple claims that iMessage is “end-to-end” secure. Neither is the case.
In iPhones, the FBI, and Going Dark, security researcher explains which threats an iPhone protects you from. As a device, it’s secure, but how you use it determines how much information you expose. In short, the iPhone is normally used as part of a system with many potentially leaky components.