Hey,
I know how you feel. I personally hate speaking on the phone to anyone who isn't family (I can struggle with friends!). However, if you really need the job then you really need the job. There's no two ways about it. Beggars cannot be choosers, but this doesn't stop you from looking around at other jobs from the moment you start working there
What I try and do, in any customer-facing/speaking scenario, is just imagine that I am not me, but a representative of the company. I pretend to be someone else who is more professional than the real-life me, and that kind of eases off - especially for you as the people on the other end of the phone will not know what you look like at all, nor what you are like outside of work.
I'm sure there will also be some kind of set script for you to follow, so you could just imagine it as reading out aloud in front of a class back in school during an English lesson.
Hope this helps and, more importantly, good luck!
MalteseMalteser