Both the PLB and spot transmit you location coordinates and rescuers can use that to guide them to you even if you are moving (more of an ocean thing).  I don't know what if any position info a sat phone provides.  Also, if I'm injured it seems more likely I could push a button on a spot or PLB than make a call and talk.  Doesn't mean a sat phone in addition to a PLB isn't a better solution, I just know I could not resist the temptation to make business calls and the reason I go is that it forces me to stop thinking and worrying about business.