Subwoofer not working?

I have an Altec Lansing sub that is an older model. When I plug my phone into it to play music, it doesn't do anything. Then I noticed that it has a speaker plug in, and I was told that you must have the speakers for it to work. I wanted to make sure that this is correct, and also I wanted to know if there was a way that I could tell if it would work before I went and spent the money on the speakers for it.