Not necessarily. A small change can be expected - by initiating a call you are changing the impedance that load the filter, that will effect the apparent impedance of the filter as seen from the line which in turn will have an effect on the VDSL signal and noise. On some phone/filter/line combinations the net effect might be zero whereas on others it could be 1 dB or so. Changing the faceplate/filter has demonstrated this. Using the very old GPO style phones also causes a significant change in some cases.
The OP however, does appear to have a problem that needs sorting.
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