There are many words which children are EXPECTED to be able to spell at different points in KS2. These are known as common exception words.
The words in the Phase 3 list are the expectation for children in Year 3.
The lists are a mixture of words children frequently use in their writing and those which they often misspell, which may be due to exceptions to spelling rules, or words which use a particular combination of letters to represent sound patterns in a rare or unique way.