How to completely silence the other party in a call on iOS

Is there a way to completely silence the person on the other end of the call in iOS?

It appears that lowering the volume while a call is in progress doesn't silence the speaker completely, unlike when a call is not in progress.

Is there a way to silence the other party completely in the call?

One to completely silence the other caller is to plug in a headphone auxiliary audio cable. You may need one with an inline mic such as this one. This tricks iOS into thinking that there is an external output device and reroutes the output audio virtually into nothingness. The microphone is also switched to use the external microphone.