I'm not sure what all it does that a phone can't do.... I only know one thing - It serves as a HomeKit Hub. HomeKit controls smart devices if you have any. So I have lights, space heaters, fans, and a few other things that I control by voice, (or touch). When away from home I can checked to see if my front door is locked and lock it if I need too.
It also has a much better speaker than a phone.... but in the end if you have an iPhone, or any smartphone, you're good to go. - JamesJM