Relationship Sex life help!!!

My boyfriend and I have been together for a year and a half, and we sometimes go through phases where we don't have sex or do anything sexual. I'm talking no make out seshs no feeling up nothing when we go through these phases. I've tried lingerie but it doesn't work, he says he does nothing for him bc he just rather take it off. Anything else that could get us back into the rhythm of things when we go through these phases again?