sob, get choked up
哽 centers on the physical sensation of choking up with emotion, especially sobbing. The given meanings both describe a tight, obstructed feeling in the throat that makes speech or breath difficult.
哽 combines 口 (mouth) with 更, which likely contributes the sound and may relate to obstruction or change. The exact historical development is uncertain.
The mouth 口 is blocked by something hard 更, like a lump in the throat that makes you choke up and sob.
For コウ, imagine a person sobbing so hard they can only cough out the sound 'koh… koh…' — the choked cough 'koh' cues コウ.