Can you get already purchased music onto iTunes?

Most of the music I own is on physical albums (cd's). Some of that music I really enjoy and would like it on all my devices. Is there a way to get those songs on iTunes or more importantly my iPhone without having to buy them all over again? I'd like to listen to them more on my iPhone, is that possible?

Sure. In your computer, you just drag it into the iTunes media/music folder. I have all kinds of stuff in their I have ripped, and recordings of my own concerts, and things I play for my students. ITunes does not always make things easy - but they can't lock you out.