You construct words by mapping consonant sounds to numbers and using whatever vowels you need to construct words.
Other people learn gibberish sentences instead. They break down the number into groups of two, three, or four and use pre-memorized words for each group of words.
So to memorize the number "102457692" they might break it up into three groups: 102, 457, 692. Then they have a word memorized for "102" (ton) and a word for "457" (rolling), and "692" (cheapen). They memorize the number as `ton rolling cheapen`.
Words are easier to memorize than numbers, even if the words don't form proper sentences.
123 is always encoded as "tomb" in my phonetic system.
555 is always lilacs.
22 is always an onion.
When an image repeats, I place a mirror at that spot.
So 123-555-2222 becomes: a tomb, lilacs, an onion, and an mirror. I store them in a certain order with a story to keep them in order.