Not exactly a reception job, but when I was an intern in the sales division, my boss asked me to memorize a 3-min long sentence of the description of our services. Interestingly, I found it easier to talk while I was trying to recall something verbatim than when doing it spontaneously. Maybe because I focused more on recalling the sentence than on my fear. So, maybe try to memorize some lines of opening until you get into the groove. maybe it will help you. Goodluck!