A friend told me it means "sexy/good looking" but I'm not sure
イケボ is a short form of either
- イケメン(cool-looking-guy) + ボイス(voice
- イケてる(cool) + ボイス(voice)
Thus, it means "the kind of voice a cool-guy has" or simply "a cool voice" This phrase is used to describe the voice and whether the speaker is an actual イケメン does not matter.
Oh, by the way, the word イケメン it self derives from the イケてる in the second form.