What is the difference between figures of speech and poetic device?

There is no hard-and-fast distinction between the terms
figure of speech and poetic
device, however, the two terms are not always
interchangeable.

The
term figure of speech refers to figurative language that is usually
colloquial or drawn from common speech. Examples of figures of speech
would be:

• Aphorisms – “A bird in hand is better
  than two in the bush.”


• Sayings/Colloquialisms – “Isn’t
  that the pot calling the kettle black?”


• Common Metaphors
  – “He was stuck on that business idea like white on
  rice.”

The
term poetic device has a somewhat broader meaning
and can be used to describe almost any intentional use of figurative language,
hyperbole, allusion, analogy, or stylistic element that demonstrates an
artistic intention on the part of the writer or utilizes a
standard poetic convention (common use of language).