I don't think this is a bug more so just a feature not added yet. When playing with subtitles there is no indication that a phantom is near as it does not show in subtitles. I tested this in survival and creative both times no matter how close I was the phantoms "sound" did not show in the subtitles. I can see this an issue for people with hard hearing so I just thought I'd report it as I couldn't find anyone else reporting it.