What do you call two consecutive consonants that represent one phoneme or sound?

The term for two consecutive consonants that represent one phoneme or sound is consonant digraph. A digraph occurs when two letters combine to make a single sound that is distinct from the sounds of the individual letters. For example, in the word "shut," the "sh" represents one phoneme rather than two separate sounds.

In contrast, a consonant blend involves two or more consonants that are pronounced together, but each consonant retains its individual sound, such as in "bl" in "black." A syllable is a unit of pronunciation that typically comprises a vowel sound and may or may not include consonants. Phoneme refers to the smallest unit of sound in speech but does not describe the relationship between the two consonants in question. Thus, the choice of consonant digraph accurately captures the concept of two consonants working together to create a single sound.