A phonogram is a visual symbol that represents a sound:
phono + gram
phono — Greek for "sound"
gram — from Greek for a letter or something written
The 26 letters of our alphabet are phonograms, but they are not the only ones. English regularly uses 49 multi-letter phonograms like igh, ch, and th to represent sounds as well.
Together, these 75 Basic Phonograms describe 98% of English words. They are the basic building blocks of written English. A phonogram is classified as basic if it is found in a high-frequency word or if it is a commonly used spelling.
Many of the basic phonograms are used in tens of thousands of words. A few of the spellings that are relatively rare are included as Basic Phonograms because they are used in common high-frequency words, such as the EIGH in neighbor and eight.
Learn more: What Are Phonograms?
See also: What is an advanced phonogram?