It is true that a secure transatlantic phone link was established during WW II between Roosevelt and Churchill that used mixers, filters, and a tone sequence recorded on a phonograph disk. The tone sequence rapidly modified the pitch of the speaker's voice so as to make it unintelligible without the decoding equipment, which was almost identical to the encoding gear and had to use an identical copy of the record (which was sent by military/diplomatic courier under heavy guard).
It was tricky to operate because the recordings had to be started at exactly the same time and run at exactly the same speed (which is still an issue with the code generators in modern digital systems).