I used to listen to readers before covid; the school arranged a couple of days training for me.
My main tip is to check that they are not just reading mechanically using the phonics, but are actually taking in what they have read. Many apparently competent readers have no idea what they've just read.
To do this you could ask them at the beginning about the characters or what has happened in the story so far, maybe using the illustrations to help. Then after they have read to you, you could ask them a question about what they've read or say "Ooh, I wonder what will happen next?" and talk about it.
If they are reading with comprehension, you can use that when they get stuck on a word. Suggest they read on to the end of the sentence and then think of a word that would 'fit' with the meaning/story.
Don't forget to praise them when they have finished, using a specific thing they have done well- e.g. "I really liked the expression you put into...., it made it very exciting".