How do you add a table in OneNote 16.24 for iPhone? On both versions of the desktop app I'm able to add a table, but in the mobile version 16.24 on iOS 12.2 I'm unable to add a table.

Most wiki's have a syntax for this, I guess OneNote is a note taking app, and so that makes it different.
Currently, Microsoft has not added the ability to create tables on the iPhone.  

Tables can be created in iOS using an iPad only (which is why I posted my comment; since deleted).  This feature has been missing since OneNote was introduced.