This will fit any standard single gang back box (not included). As an extension socket, you can either run 2 lines to it, 1 to each socket, or run 1 line then link between the 2 sockets to use like a doubler.
eBay
3.5mm Female To Female Coupler Stereo Audio Adapter Extension Straight Connector for Dual Channel Stereo Headphone Jack Cable
Aliexpress UK
1xTYPE C Two-in-one splitter Adapter. Female Type: Type C interface, Aux Jack for earphone. Achieve charging and headphone connection simultaneously. Wide range of applications - Main function is data/video transfer or mirror on TV/PC and charging.
eBay
Vention Type C to Dual 3.5 Jack USB C to 3.5mm Aux Double Earphones Audio Adapter for USB-C Tablet Phone Laptop Jack 3 5 Cable
Aliexpress UK
This wall mount dual phone jack in ivory color is the perfect addition to your home or office. Designed by Ace and made in China, this telephone model #3048270 is a reliable and efficient way to mount your phone. The sleek and modern design of this wall mount is perfect for any setting and will help to keep your phone safe and secure. The wall mount is easy to install and can be completed in just a few minutes. The dual phone jack allows for easy access to your phone and will help to keep your space organized. This wall mount is a great accessory for any home or office and is perfect for those who want to keep their phone easily accessible.
eBay
2Pcs Y Splitter Adapter Connector Stereo 3.5mm Audio Jack Male to Dual 3.5mm Female Double Plug for MP3 Phone Earphone Headphone
Aliexpress UK
It is compatible with Samsung Galaxy Note10, Note 10 Plus, Samsung Galaxy S20, S20 Plus, S20 Ultra, Samsung Galaxy Note20, Note 20 Ultra, Samsung Galaxy S21, S21 Ultra, Samsung Galaxy A72, Samsung Galaxy S10, Samsung Galaxy Note 9, Samsung Galaxy S10 Plus, and Samsung Galaxy A12.
eBay
1 To 2 Dual Earphone Headphone Splitter Cable Standard 3.5mm Jack Universal Audio Cable Y Splitter For Audio Earphone Splitter
Aliexpress UK
Connector Type: Type-C. Cable Type: Tangle Free. Color: White. Condition: New.
eBay
Hi-end OCC HiFi 4.4mm to Dual 6.5mm Cable Balanced 4.4mm Jack to Dual 6.5mm TRS Jack for Amplifier Audio Cable
Aliexpress UK
As an extension socket, you can either run 2 lines to it, 1 to each socket, or run 1 line then link between the 2 sockets to use like a doubler. While we do what we can to resolve any rare problems, we hope we can count on your patience and understanding.
eBay
3.5mm Headset Splitter Adapter Cable TRRS 3.5 Male to Dual TRS Female Jack Mic Headphone Audio Extension Cord for Computer Phone
Aliexpress UK
Quantity: 1 x 2in1 Adapter. This unit has two ports and is compatible with a range of Apple iPhone models, including the 14, 13, 12, 11, X Pro, and more. - Compatible with iPhones series 13, 12, 11, X, 8, 7, 6.
eBay
Dual 3.5mm to 3.5mm Jack Headphone OFC Upgrade Replacement Headphone Cable Pure Copper Plated With 5 u 24k Gold Plug 1M 2M 3M 4M
Aliexpress UK
SABRENT USB to 3.5mm Jack Audio Adapter, External Sound Card, USB Headphone Adapter, Headset Adapter for PC, USB DAC with TRRS, Compatible with PC, MacBook, Laptop (AU-MMSA).
eBay
Vention Audio Splitter USB C to Dual 3.5 Jack Type C to 3.5mm Aux Double Earphones Audio Adapter for USB-C Tablet Phone Laptop
Aliexpress UK