Why isn't my modular plug working from my phone

Why isn't my land line phone working with a modular cord plug I installed.

Telephone cords are made with a twist. In other words the ends are rotated 180 deg. Line the plugs side by side and the color sequence should be reversed for the other plug.

Usually a phone might get dial tone, but won't be able to dial out and you can answer it. Occasionally nothing works. Depends on the phone.