There are two dimensions to phonology in spelling:
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graphemic awareness;
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phonemic awareness.
The graphemes are a limited set of of one-, two- or three letter strings that represent the phonemes of English.
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Two-letter single graphemes (like <wh>) are called ‘digraphs’.
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Three-letter single graphemes are called ‘trigraphs’.
However many letters compose a grapheme, it is still a single unit of spelling.