Android phone/Pandora/stereo set-up

3.5mm jacks are not all the same, even if they have the same number of rings. You need to get a 4 conductor cable.

"You still should have gotten at least one channel using
the mono cable? Was it pressed all the way into the jack?"

Not in this case. Mono is 3 conductors, not 2. And stereo is 4 conductors, not 3. You need to get a cable that has 3 rings and is labelled TRRS. If it doesn't say TRRS, the cable won't work.

Radio shack has what you need.about $8 depending on length

Do you have a protective case on your phone? If so that could be the problem as it will prevent the cable from going in all the way.