I was a TA / helper in primary for twenty-five years, and it can be a lovely environment to work in!
If you don't get to know in advance what Phase the group is on, I would err on the lower side rather than higher. If they ARE good at it you can tell them how amazing they are!
Go slowly, and be prepared for them to possibly not pay enough attention, not understand etc. (Though in my experience secondary don't always pay that much attention either!)
You may be told in advance a suitable 'big book' you could use: make sure the group can all see it; invite them to tell you what they know/can see on pages, both text and pictures. I would guess the main interest from the panel will be how you interact with, control and engage the children. (I assume they KNOW you are coming from secondary?)
I always feel a touch of humour, or at least some lightness, can help. Maybe even TELL the group you worked with 'big' children previously, and give mock surprise at how 'tiny' these children are, which hopefully, they will indignantly deny!
Have your own books or suitable props available in case needed; and may be something from your secondary world?
Re Phonics: in the MN Book Reviews, 'Children's educational books and courses' section, the Oxford Phonics Spelling Dictionary I think is a useful volume, and could be shown to the group possibly.
Above all, ENJOY it, and ensure the children also enjoy it!