Does an r controlled vowel needed the letter r?

The 'r' controlled vowel /aw/ is a phoneme. It can be represented by many different graphemes. Many of these have an r letter within this grapheme, but not exclusively

• In the word sword, it is represented by the digraph or.
• In the word, saw, it is represented by the digraph aw See, the same phoneme, but no R letter in the grapheme
• In the word, explore, it is represented by the trigraph ore.
• In the word bought, it is...