In simple terms:
The pair from your house goes to the old cabinet. It is then connected to a tie pair which goes to the new FTTC cabinet and when it reaches there, the VDSL and voice are split. The VDSL is dealt with at that point and fed back to the exchange over fibre, whilst the voice signal is routed back to the old cabinet on another tie pair where it is connected to the original pair from the exchange.
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