I am an Army signal officer with 5 deployments. The military considers cell phones inherently insecure and not a mission asset, regardless of what you may read.
Is that because military-purpose communications is insecure over 4G, or because modern smartphones, full of adtech malware, make it all to easy to leak your location by accident?
It's a variety of factors. Information leaking is one, but a big one is the lack of control. DoD does not control any significant part of the present cellular network, so it might be useful but it oughtn't be part of your critical systems.
