To set your mixer up to receive phone calls for your Podcast/Radio show you need to setup what is known as a Mix Minus. 

A Mix Minus allows you to setup a Mix that has a specific input removed. For a caller on your show this will allow them to hear all audio except their own voice back to their phone. 

1) Most software such as Skype, Discord and Microsoft Teams (as an example) will use USB Channels 1 and 2 as the default input and output device so ensure that channels 1 and 2 are using the Card as the input source. When you then take a call on your software you should be able to see an input level. 

2) Create a mix bus For all audio that you want sent back to the caller. Send these signals to the bus. 

TIP: As the software will require a Stereo input, we would recommend stereo linking 2 bus channels. 

3) In the Routing > Output menu, assign the stereo mix bus for the caller to Output 1 and 2.

TIP: We would recommend doing this as Post fader, allowing you to control the level to the caller using the fader. 

4) In the Card out menu, Assign the outputs you allocated for the callers mix bus to Card 1 and 2. The caller should now be able to hear everything except their own voice. 

5) Record your show in your chosen DAW.