For as long as I can remember[0] the DoD and all DoD contractors have required those with cellular phones to leave them outside of secured areas. Phones have not been and continue to not be permitted inside secured areas for any reason, even if they are powered down.

It might just be that the DoD is paranoid, but I'm not so sure about that.

[0] That is, since long before smartphones and phones with local audio recording ability were commercially available.