When talking to Alexa, attempt to use the wake word (Alexa) and wait for Alexa to wake up (and optionally emit the beep). After Alexa has woken up, delay speaking to Alexa for a few minutes intentionally. It seems that Alexa takes a while to adjust to the surrounding noise when woken up by the wake word such that by waiting before uttering the intended phrase, Alexa seems to recognize the upcoming phrase more easily.