A search for Phaser results in Phaser CE and … Phaser 4. On Discord it was confirmed 4 is not ready yet (the result indeed points to 4.0.0-alpha). The current version to use is Phaser 3.23.
Not sure what the reason is for having Phaser 4 up there, but I don’t think that is the best choice at the moment as it is still under development.
(thing also is, I just pointed about 300 students to cdnjs.com to get the current Phaser 3 version… )