I wonder what’s the chance the was random. With all the planes that have made holding patterns over the years, I’m sure some look phallic by chance. Or maybe the tower usually makes sure not to accidentally draw that?

Usually they do a racetrack.

Yep. 90 degree turn, 90 degree turn, hold.... 90 degree turn, 90 degree turn, hold... Repeat as long as necessary. From day 1 of flight training. It's also standard when waiting your turn to land, maintaining altitude to help keep different planes in their envelopes. Circles run the risk of losing altitude and/or airspeed.