Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
I am sorry to hear about the problem you report. It may be that one of the devices has ceased to be operational enough to be a useful or usable Bluetooth device.
The best test you could do at this point, would be to try to connect the phone to another, different, Bluetooth device. If it does connect OK to a different and other device, then the phone is not 'broken' thank goodness.
If the phone does not connect by Bluetooth, then double-check that its Network settings show that
1. WiFi is Off.
2. data networking or fast networking is Off.
3. Bluetooth is On, and pairing is allowed (with the specific device, at least.)
If all three are true, but connecting (to more than one Bluetooth-capable device configured correctly for connecting) according to instructions still fails, then the phone may be defective.
The other way, would be to try a different handheld that is Bluetooth-capable, with the KX-TG78. If it also fails to connect, then most likely the KX device is where the defect is.
Let me know what happens, what you think, and if I can give you further advice or assistance, just ask. Thanks.