I think you mean, is it some kind of 'set' phrase, almost like an idiom.
Well, not really, but because of the influence of Existential Philosophy, "purpose to my existence" is almost a cliche among those seeking some 'meaning' to their lives and the reason for human existence.
It's better to think just in terms of the word "purpose" and the prepositions it takes - so:
find a purpose for (find some use for) something.
have a sense of purpose in doing something - that is, have a goal or aim and feel resolved to reach it for some important reason.
and as above,
purpose (some point, reason for) to my existence
There are probably other prepositions as well, but these three come to mind.
Student or Learner