Recently, Phabricator changed the plus icon in its toolbar to instead be a star. Presumably that is to reflect that the menu is no longer restricted to creating tasks, but serves as a configurable "favorites" menu.
A star in the toolbar most commonly means "save/favorite whatever I am looking at right now", which is absolutely not what this button does. Unless you notice the dropdown arrow, you are unlikely to think to click it. Even with the dropdown arrow, it's not what many of us would expect to press to "create a task".
The icon should change. I'm not sure to what, but even an ambiguous web "hamburger menu" icon would be less misleading.