Adding Aux input to Linear Series LS7600CD Player

Hopefully, there is a diode or some resistance close by in that circuit so that you don't lose the output of your CD player or, burn up the output of your phone. It might be safer to use just one signal source at a time, leaving the other unpowered.

An alternative to using an additional device or player might be to solder on a Bluetooth board into the CD player's input circuit. That assumes that your additional playing device has Bluetooth capability. The Bluetooth boards can be had for less than $5.