I worked for a government organisation in the UK 25 years ago, initially on a casual contract. When I applied for a permanent job in another department, my stammer was so severe at the time that I classed it as a disability, which meant I was guaranteed an interview (I probably would have got an interview anyway). While in that post, it wasn't really my job to answer phones, but some colleagues expected me to if they were busy and the person whose phone was ringing wasn't there. I never did until I was comfortable doing so. It was never a problem officially.