Is there a term to denote writing numbers in words rather than as digits?
The phrase spelled out is sometimes used; eg,
In your paragraph, spell out the digits under 10.
This usage is from the sense “To write or say the letters that form a word or part of a word” or the sense “Of letters: to compose (a word)” of the verb spell.
Longhand is the word I have heard used for this, though the definition does not specify the writing out of numbers.