Sentence:  Destroying the lich without destroying the <WSD>phylactery</WSD> first just allows the lich to regenerate its body over time (or steal someone else's) and it really pisses them off. With the intense connection a lich has with its <WSD>phylactery</WSD> if it gets destroyed the lich will know instantly. 
Meaning of the word marked with <WSD> tags:  An enspelled object used (by such as a lich) to contain and protect the owner's soul.