The HK Onyx doesn't have a microphone, so it can't be used as a speaker phone.
You can use a Jamebox or Beats Pill as a speaker phone. The Onyx is my wife's, and it seems to have the best sound of the three. I have the Beats Pill and I prefer it over the the Jambox (which my mother in law uses). The Pill has a built in charger to keep other devices charged and gets louder than the Jambox, but the Jambox is a cheaper option, and if you want to use it to take/make calls, any sound quality difference won't matter.