This is blatantly incorrect though. The NSA actually set up the DMCC phone system specifically for this purpose. They are phones with 100% of the infrastructure already set up for communicating classified or sensitive information even while abroad and they are hardened enough that they are generally considered unclassified when powered down. They come in a DMCC-S (secret) and DMCC-TS (top secret) flavor. Any somewhat senior member at any agency or department that regularly interacts with classified information could request one of these devices. They provide cross agency encrypted call, text, and other capabilities at all security levels.
https://www.disa.mil/-/media/Files/DISA/Fact-Sheets/DMCC-TS-...