system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can a phone line be deemed secure?

Title!
gpt
Most of what you see is a Hollywoodism where they declare a line to be 'secure'. There are multiple places where someone can tap a phone call.

The phone itself can have a listening device attached to the microphone and speaker, the line from the phone to the wall jack, the wall jack to the demarcation point, from the demarcation point  to the various points on the telco's network, and again all the way to the recipient's phone. 

In government and military terms, access to the physical device and lines are protected, and often the phone line itself is encrypted using various digital or analog encryption technologies.