A Sony compact from 2016 didn't have to house today's hardware.

Any phone today is larger and thicker than my Samsung S4 from 2014. Any phone today would also outperform it by orders of magnitude.

This Enough phone doesn't look any thicker than many phones today.

Unfortunately a headphone jack is required by a small subset of users, just like small phones. So wanting a small phone and a headphone jack is an even smaller subset of users.

Though I think Unihertz does headphone jacks even on their Jelly phones.

Unihertz also understands that phone width is a bigger issue than thickness (they probably have some ratio they've determined works). I can't reach across my Pixel 5 one-handed.

Edit: from their own website, the Enough phone is less than 12mm thick. That's on the thicker side, but not world-ending thick.