You'll sort out the sound in due time.
No really possible.
A "call-in" show by definition uses the telephone. Quality is dictated by the phone connection from the caller.
Only way to get good quality audio is to have every caller use a known audio setup, and that's hard enough to get right for a single guest.
At least levelling, and something to shift the tone up or down, that can be roughly done in a second
I use to do this with speakers at conferences, you'd be surprised at the difference in volume and tone from person to person even with the same setup - especially if the languages change!
We did not listen so much as simply stare at a simple "SEA" LED display with frequencies plugged into the output... One knob would adjust the volume if the speaker would go into the orange or be too low, the other shift the tone left or right if he was sqeaky or bassy.
It was really simple, you'd do it without even thinking by the 10th speaker.
anything above that is too complicated for real life.
I've just listened to a few podcasts of Dave Ramsey, a popular talk show host in the US, and despite him having a million dollar studio, some calls are barely understandable...
Perfect is not possible, good enough should do it, she'll be allright, job' a good one, Mate’s rates sound, No dramas.