Really good advice from @beautifulstranger101 - baby steps really helps with stuff like this.
The stuff you've described from your childhood isn't "small" or insignificant - it's traumatic. It's really hard to hear how down on yourself you are. You brought in biscuits - win! You went to the team canteen meal - win! Both of those acts were brave. You dodged out on the Xmas meal out - so what. Can't win 'em all.
You're also doing really well with the job - making phone calls to senior management can be nerve wracking. If you were doing a bad job, your line manager would already have brought this up with you (you don't wait til the probationary review to address these things.)
A job I was at a few years ago, we had a morning and a midday conference call with colleagues and the dept head (so think about 4 grades above ours) and it could be very overwhelming for some. I had a colleague, same grade as me, on another site and she had social anxiety and always ducked out of doing the calls. Eventually me and other colleagues basically said "you need to just tough it out because the longer you avoid it, the more scary it will seem." So we made an arrangement that I would go into the call silently so I could hear what was being said and if she got flustered I could instant message her what to say. Like "We've allocated 5% of our resource to Dept Y as they are currently running well under target" or "We'll be reoptimising everyone's breaks and lunches to address the decrease in volume and encouraging team managers to do offline activities with their staff."
It sounds like you're handling that side of things very well! But it makes me think could you roleplay some "small talk" stuff with your DH?
I was a confident child through primary school but the dynamic at home changed pretty much with my transition to secondary and I became very shy and withdrawn. In addition I felt very different to other girls who were interested in hair and makeup and boys and weddings and celebs. Finding my "tribe" helped enormously with my confidence. I am now happy making small talk with people who aren't "my people" (and no shade on them, everyone is entitled to their own interests and outlooks!) - I've just learned to keep it very superficial, as plenty of PPs have suggested and use reflecting questions.
Also, compliment people! When you're at the checkout and the assistant hands you your change, say "Ooh I love your nails!" or whatever. Same thing when a colleague arrives wearing a different hairstyle or funky shoes. Everyone likes to be complimented on their excellent taste!
Finally, if you're still struggling with the physical symptoms of anxiety, I'd recommend downloading either Calm or Headspace onto your phone (both free for the basic version) and listening to a 5 min meditation in the morning (pref before the chaos of getting kids ready for school!) and at lunchtime in the loos/park etc. Give yourself a chance to breathe.
Best of luck OP and I really hope things improve for you in 2020. You are absolutely doing the right thing by reaching out for support - that tells me you WANT to change things.