YES, DECODING is harder than CODING.
Let's assign integer numbers to letters according to their place in the English ABC (a=1, b=2,...,z=26.)
We then "code" a given word by 2 parameters, e.g:
Once you find how the coding was done, you will understand that
a) There is no one-to-one-correspondence between the word
and the ordered couple, so STAR, ARTS and RATS produce identical couples.
b) The correct decoding of a meaningful phrase might be possible.
NOW DECODE THE FOLLOWING PHRASES
(only one 5-letter word - all other words less than that):