What is the twin phono used for?

A Twin Phono is also known as an RCA connection and carries two mono signals across each Phono connector, which are combined in audio equipment for stereo sound.

3.5mm Stereo Jack to Left and Right 2RCA Plugs

• SAMZHE 3.5mm Male to Dual RCA Stereo Audio Cable - TRS to L/R Channel Adapter for Hi-Fi Systems, Amplifiers, Audio Devices, Laptops, PCs.
• This RCA to headphone jack offer incredible audio clarity over all lengths to provide a versatile connection between hardware for all your stereo audio needs. The slim metal case connector allows you to plug it to your source device without taking off your mobile phone case.

Fit All Devices of 3.5mm or 2RCA (Red and White) Audio Ports

3.5mm Devices:

Compatible with MacBook Pro, Macbook Air, iPod, iPad, PC, laptops, smartphones, tablet;

Compatible with Walkman, Discman, MP3/MP4 players;

2RCA Devices:

Compatible with Amplifier, Speaker, TV, Car Radio, DVD, AV receiver;

Compatible with Subwoofer, Dolby Digital Receiver, DTS Decoder, Mini Disk.