What is the meaning of following sentence ? I have trouble understanding with the way it's formulated

Here is a longer quotation, ending in the sentence you ask about:
Goodreads Frankl quote

A given symptom is responded to by a phobia, the phobia triggers the symptom, and the symptom, in turn, reinforces the phobia.

That is the "circle" the author refers to in the sentence in question. The author is saying that the neurotic's preoccupation with himself, whether that takes the form of self-pity or self-contempt, can't break that circle. Rather, a transcendence, or moving outside of the circle is required. The rest of the quote speaks vaguely of some ways of doing that.