With an iPhone (at least a newer generation, you don't say what you had) my understanding is that it's pointless selling parts, the major parts all have "ID numbers" and "know" which iPhone they were built with. They won't work being plugged into a random phone. There shouldn't be a spare iPhone parts market anymore.
If you used the "find my iPhone" feature, you should have been able to declare it as stolen and put a message to that effect on the display. Nobody's going to get their daily drug dose, it was wasted effort. Android phones on the other hand...