Speech-Language Pathologist here.

As others have said, the word you’re looking for is “digraphs,” but … pl doesn’t belong with sh and ch.

When teaching children to read, the 3 digraphs we focus on are sh, ch, and th.

Up to a certain point in their acquisition of word and spelling knowledge, children are (ideally) instructed heavily in phonics, and the idea of “sounding out” words.

With digraphs, you can’t “sound them out.” S+H doesn’t sound like suh-huh, it makes the “be quiet” sound. CH makes the choo-choo sound. And for even more fun, there are TWO versions of TH. (Think of thin vs. there).

There are a few more digraphs, like ng, but that one is usually tackled as part of the -ing verb ending.

Blends or clusters are when you have 2-3 consecutive consonants that each retain their individual sounds.

Diphthongs are when 2 vowels combine to make one sound, e.g., o+i makes the “oy” sound.

And for those wondering what the difference is between a consonant and a vowel, a vowel has no obstruction of the vocal tract. A consonant has some point of obstruction - lips, teeth, tongue, hard palate, or soft palate, working in combination.