Morphemes are indivisible units of meaning, whereas phonemes are units of sound. As an example of a morpheme, can you find a connection among the meanings of the words below?
twin
twice
two
twelve
twenty
between
twine
twist
twig
TW means 2. If you're curious or need proof, the Online Etymology Dictionary is a fabulous resource for discovering the origins of words and units of meaning: https://www.etymonline.com/.
Providing explicit instruction on both morphemes and phonemes can help students decipher words and spell correctly. TO, TOO, and TWO sound alike, but when students know that TW means 2, it helps them select the proper spelling and prepares them to decode new words they might encounter, like betwixt, twain, and entwine.
What's more, its just plain fun to know how our language works. A visit to the Online Etymology Dictionary often pays dividends immediately in appreciating the word of interest and later in decoding related words encountered in the wild.
For a more comprehensive discussion of morpheme types, visit https://www.ntid.rit.edu/sea/processes/wordknowledge/grammatical/whatare.