They are. You may be seeing more exploits in general because there is monetary incentive to find them, but iPhone is more secure in general especially when it comes to malware. They also have 5 or more years of support for devices and historically patched very old versions for security issues. Unlike android where 10% of the users are on the latest update, if the carrier even supplies it!

And it is. iPhones have fewer exploits, and (in general) provide longer support with updates fixing them when they occur.

citation needed.