If you're seeking a simple way to sum a left and right line level RCA audio signal into an iPhone or iPad, the Sescom LSUM series is the right cable
Sescom SES-LSUMXLR iPod/iPad Summing Cable Dual 3-Pin XLR Female to 3.5mm TRRS Male for Apple Lightning Adapter - 3 Foot
Audio for Photo Full Compass Systems
Smartphone Cables
Sescom Catalog 2016 by Sescom - The Audio Source - Issuu
Comica CVMV01CP(4.5m) Omnidirectional TRS Lavalier Microphone for Cameras - 14.7 Feet
Sescom - Authorized Dealer, Rubber Monkey
3.5mm TRRS Male cables, Rubber Monkey
Comica CVM-D02 (B4.5M) Dual-Head Lavalier Omnidirectional Condenser Mic for DSLR/GoPro/SmartPhone - 14.8 Foot - Black
Trrs - sprawdź!