In searching about this word, I found sites using "Anglo-Saxon monosyllables" as examples.
I found AHD definition, which did not add much, except tor link to Appendix which I did find

Indo-European Roots

To think. 1. frantic, frenetic, frenzy, –phrenia, phreno-; phrenitis, from Greek phrn,
the mind, also heart, midriff, diaphragm. 2. Extended zero-grade root form
*gwhr-d-. phrase; holophrastic, metaphrase, paraphrase, periphrasis, from Greek
phrazein, to point out, show. (Pokorny ghren- 496.)

The part where "phren" is said to be related to the diaphragm explains "phrenic" as name for
the vital nerve that controls the diaphragm. Polio patients often had paralysis of phrenic nerve
with inability to breath normally, and so had to be placed in "iron lung" which only oldtimers now

"{hren-" also reminded me of ancient jokie about the guy who was very much interested in phrenology,
the alleged science correlating head shape with mental ability. When he told his girl he wanted to break
a date to go to a phrenology lecture, she told him to flip a coin.