A:Answer I have never used my smart phone with this sound bar. I have it plugged into the optical port on my Samsung TV, and I set the audio output on the TV and the sound bar input to both be this port) and I can adjust the volume with the Fire Stick remote (or the TV remote). The sound bar does have a remote, but I never use it. The Fire Stick is plugged into the ARC HDMI port - I have no idea if that matters, but that's where I put it. I don't know if Alexa would control the sound bar as I've never tried. However, since the Fire Stick remote works to control the sound level, I imagine that Alexa will do that as well via the Fire Stick.
Note: I tried using the optical port because I was running out of HDMI ports, and it's worked just fine, so I left it there.