The fully phonetic version: hiepojimnia
heard as hiepojimnia
spelled hypogymnia
Every sound is right. The spelling is hypogymnia.
What the ear did
Three separate conventions have been overturned at once: hy for the sound of high, g for the sound of j, and y for the sound of i. All three are Greek in origin and none of them is audible.
H-Y-P-O-G-Y-M-N-I-A
The full entry for hypogymnia covers the name itself.