I would like to help some players out, but I currently have 5 humanity active and I don't want to lose it.
Will I lose my humanity if I die as a phantom in another players world?
If you die as a phantom you only return to your world where you last rested at a bonfine. There is no penalty to dieing as a white or gold phantom. In addition as a Blue phantom you also do not incur a penalty. However if you invade others as a Red phantom you "die"(Drop souls and humanity) where you were when you invaded but you remain human and return to the bonfire.