The Collaborative International Dictionary of English v.0.48:

phren- \phren-\, phreno- \phreno-\, phreni- \phreni-\, phrenico-
\phrenico-\(fr[e^]n- or fr[=e]n-), n. [Gr. frh`n, freno`s, the
   midriff, or diaphragm, the heart (as the seat of emotions),
   the mind.] (Anat.)
   A combining form meaning, of or pertaining to the diaphragm,
   the mind, or the brain; frenic. --Stedman.
   [PJC]