“This achievement recognizes that Apple has transformed how security is traditionally delivered,” said Ivan Krstić, Apple’s vice president of security engineering and architecture. “Prior to iPhone, secure devices were only available to sophisticated government and enterprise organizations after a massive investment in bespoke security solutions.
https://www.computerworld.com/article/4137985/nato-approves-iphone-and-ipad-to-handle-classified-info.html
NATO approves iPhone and iPad to handle classified info

The okay means Apple's products are the first and only consumer devices to have achieved such compliance.

Computerworld