That can be demanding work at times, I can understand because I have done phone work myself, I got a training position in a Social Housing Complaints Dept. shortly after leaving school, taking phone complaints about leaking pipes and what not! I also worked on a reception switchboard in another job receiving calls for about twenty staff. I was in at the deep end both times. I have had several jobs that required dealing with the public face to face or over the phone - and I am a somewhat reserved person by nature.
I see you are searching for something else, and that may be what you need to do, nevertheless while there make it work a bit for you by developing your skills even if you want to look for something else in the meantime.
There are a number of things that might help while you are in this job. Having a scripture verse or two committed to memory is very powerful because the Holy Spirit can use these to calm your nerves, all we need to do is agree with the truth in these scriptures.
As others have said begin your day with prayer, acknowledge your dependence on God, and affirm there will be no call that God will allow that He won't also give you the resources to handle, and ask God to undertake for any misunderstandings = Faith in Future Grace.
When you have a difficult caller, first of all
stay calm. I agree with what someone else said you have to keep your expectations low, while customers won't always be nasty, don't expect much gratitude, some people get something solved and just hang up. You've been doing your job however they end the call.
As those calling don't know you personally, any impolite things they might say, however they might seem should never be taken as a reflection on you, or ruminated on, dismiss them from your mind. Nevertheless there is a limit to what people can take in terms of rudeness and everyone is different, so ask your supervisor and others who have been in the job longer about handling that sort of thing, and when it is appropriate to end a call - you may need to issue a warning that continuation of abusive language will lead to their call being ended. Deal only with the actual business substance of the call, ignore overly familiar remarks and quickly move on with asking any details needed from them to help them, adopt a 'no nonsense' manner when appropriate - use their surname a few times - Mr. Jones or whatever, in the course of the conversation as fitting. Most members of the public if they have been a bit rude often come to their senses and remember they need to be polite to some degree to get what they want,
they know this from previous life experience.
Have what you need to handle their questions close to you if possible, or know where to go to get it if its filed away, become adept at calling up files on the computer if you are working at a terminal. Take control of the call from the outset, get the necessary info all up on screen first. Keep them informed of what is going on at intervals eg. "Ok I have cancelled that for you" or whatever. Ask as many questions as you need to confirm you know what they are ringing about.
Here are some more tips. I hope something in these will help.
https://talkroute.com/10-steps-to-handle-a-tough-customer-on-the-phone/
