They also sell smart outlets, back massagers, and garden sprinklers on Amazon. That doesn't imply people would find them handy in their phone.
I think it'd be an easier pitch in the watch though as that's where they are already shoving most of the health sensors (and have wrist temperature monitoring already).
You can also read it in 2015 Tim Cook's 3D touch announcement voice or Zu announcing the ZTE device with a 3D screen in 2017 or whoever at LG announced the wide angle lens, got meh to bad reviews about it, and then it took off afterward anyways.
My point here is I'm not saying it can't ever be something anyone would want because of that rather something selling in another device on Amazon has no weight one way or the other on whether it'd be a good thing to add to a phone.
I think it'd be an easier pitch in the watch though as that's where they are already shoving most of the health sensors (and have wrist temperature monitoring already).