From memory the phasing sound is 24 meters just like her terror radius, you just have to be outside of the husks terror radius to hear it. Had you just exited the terror radius of the husk when you started hearing the phasing sound? If you had then it may have just given the perception of her having to be really close to hear the sound. If she was using any add-ons that increased her movement speed while phasing they may have also given the perception that she was close when in reality she just caught up quickly.