Final answer:
The phrase 'motiveless malignity' coined by Coleridge is used to describe Iago's nature in 'Othello' and similarly reflects the state of the Mariner in 'The Rime of the Ancient Mariner.'
Step-by-step explanation:
The literary phrase coined by Coleridge that describes the nature of Iago from Othello and also reflects the state of the central character in the beginning of book two of The Rime of the Ancient Mariner is "motiveless malignity." This phrase encapsulates a sense of evil or malevolence without clear reason or purpose, which can be seen in the actions of both Iago and the Mariner.