If you have an antenna in the dash it may be for the old WDCT wireless handset. This device also operates at 2.4GHz and would be suitable for BT. Unusual that your phone was prewired with the antenna too, but then the US market cars are differnet to the UK cars.

you could find the lead that is connected to the WDCT antenna, plug it into your ULF/TCU and see what happens.

You can note down the part numebrs of your antennas and type them into RealOEM to find out which versions you are equipped with.

You may find your newer antenna relocated to behind the ashtray will give you the performance you are looking for.