There doesn’t appear to be a breath phoneme.
Edit: The br phoneme is the phoneme used to indicate a breath. However, it is not implemented in all the voicebanks. For example, it’s in Saki AI (Lite), but not Eleanor (Lite). Also, there’s no documentation for this phoneme.
There is an Aspiration Output in the Pro version, but that appears to isolate the “whispered” portion of vocalized sounds so they can be mixed in the DAW, not actual breaths.
There’s a hack of using the hh phoneme, but it’s not optimal.
It’s possible to add just record breaths and add them in the DAW, but a breath phoneme inside Synthesizer V would be helpful in tuning the performance.