Seems everyone jumped to conclusions about this article.

Yes, iPhones are blocked because they lack security. This is military, so they aren't worried about basic malware. They are worried about government level security issues (Pegasus, etc...). And let's be blunt, on this level, Apple keeps showing that they lack security in the real world situations. Yet the latest of a long list of iPhones being targeted and hacked.

Now, where people seem to be badly jumping to conclusions is that the article points out that "many" devices will be banned, so no, I doubt the latest Samsung Galaxy phone will be allowed. They are most likely going to require people use a Samsung Tactical Edition smartphone. These are designed for military usage and prevent phones from being secretly turned on for recording private conversations by hacks like Pegasus. These phones have been around for a few years now, and have likely been thoroughly tested and approved now.

This isn't some knee-jerk patriotic requirement, but a real understanding of what is and isn't a secure device, combined with the fact that Korea has to deal with a more and more aggressive China. They need real security for real world military.