Being actually a native speaker, and keeping in mind that the OP might be mexican (which may have some subtle consequences), my understanding of the title is that he wants to sell a "piece", i.e. a part, of a Jolla phone. Could be the battery, the display, or a piece of broken plastic

Admittedly my spanish, together with a few other languages, are getting actually worse every day but put it this way: I would not sign a contract based on the thread title