This systemd unit is needed in order to cope with having both haegtesse and wys installed at the same time. We can have the audio unit be brought up with only a WantedBy relationship to default.target.
Systemd can resolve mutual Conflict options by favouring a unit which is RequiredBy over one which is WantedBy. So, we can have haegtesse.service and wys.service Conflict with each other but we don't want default.target to have a RequiredBy relationship with either as that would mean default.target will fail if the RequiredBy unit (wys.service) fails. By inserting phone-voice-call-audio.target between wys.service and/or haegtesse.service, we can use systemd to resolve the Conflict option while also maintaining only a WantedBy relationship with default.target.