dt cryptic 12.10

[sarumite]

Again stuck on one!

27a Rewrote, or inserted a phrase justifying one's existence (6, 1'4) ?a?s?e ?'e?r?

Probably staring me in the face, but I can't see it.

[Quizmonster]

Raison d'etre.

[sarumite]

Of course Quizmonster, and an anagram for such a well known phrase. The e at end of first word hasn't helped - so will look at that one again. Many thanks S.