This discussion helped me fix same problem. Let me put it succinctly. The phone does not forget, it tells your bluetooth device "forget about me and never try again". So the solution is to make your BT device try again. Put it into "pairing mode" and then you will see it on your phone again. You can Google for a phrase like "plantronics bluetooth pairing". That is how I found out how to get my device back into pairing mode. Usually something like "turn it on and hold down the call button until the LEDs flash and then you will see the request on your iPhone".