A phoneme is a distinct, single sound that is used in the speech of a particular language. Phonemes are the smallest units of spoken language, and we combine phonemes to make words.
A phonogram is a visual symbol used to represent a speech sound in writing: t, m, oi, ch, igh, etc. Phonograms are also referred to as graphemes. They may contain only one letter or more than one letter.
The spoken word "cheek" has three phonemes, which you can hear clearly if you say it aloud and separate it into its sounds: /ch - ē - k/. The sounds, not the symbols that represent them, are the phonemes. And this spoken word is written with three phonograms: ch, ee, and k.
Similarly, the spoken word "though" has two phonemes, /TH-ō/. When we write this word, encoding its sounds into a visual form, we use the two phonograms th and ough to represent these phonemes.
Learn more: What is a basic phonogram?