Use One of These Apps to Encrypt Your Calls, Because Your Phone Won’t
via cisa.gov
Short excerpt below. Read at the original source.
When you make a regular phone call from your mobile device, it is not guaranteed to be secure. Cellular protocols are not encrypted end-to-end, meaning that audio could be intercepted along the way, such as by carriers, law enforcement, or threat actors. You may have worked to ensure end-to-end encryption (E2EE) for your text messages […]