It's quite easy to spot a stage 3 Phone-zombie. They are easily distracted even in conversation, shifty eyes, can't focus on tasks, bad sleep habits. This is a huge limitation in life and a pretty crappy way to exist, in my opinion.

People who are rude in public are just unhappy with their lives because they haven't found deeper meaning, so they try finding comfort in becoming a phone-zombie.

It's a vicious cycle.