Phonbloks would never have worked. Phones are all different shapes and sizes, so you just run into tons of compatibility issues whenever you want to upgrade anything, as new components will be larger than the old ones. Technology just doesn't progress in ways that nicely fits into form factors from five years ago, fingerprint reader, FaceID, multiple cameras, wireless charging, etc. None of that fit into a block model. Phones are also a weird market place where people give up headphones and replaceable batteries if it makes their phone 1mm thinner, so a big bulky modular device would really have much chance against the much sleeker competition.

Fairphone is a much better compromise, it's modular and repairable, but in a way that is actually practical. Turning everything into LEGO blocks looks fun in concept images, but nobody would want to use that.

Moto Z is/was another more interesting approach, instead of making the phone itself modular, it has some contacts on the back to dock extension modules. So you get extensibility without really changing anything about the phone itself.