What does Isaiah 23:5 mean?

The oracle against Tyre began by measuring the loss of the great city as felt by all who depended on it. This deep loss will be felt from the sailors who worked on the sea to those who grew rich from the industry the city provided. Even the sea itself, in a symbolic sense, will feel the loss (Isaiah 23:1–4). Now Isaiah adds that there will be anguish in Egypt when the news reaches them that Tyre is destroyed.

Isaiah has already mentioned the revenue that flowed into Phoenicia from the grain of Shihor (Isaiah 23:3). This area was likely a branch of the Nile in Egypt where the grain was grown. Egypt had a long history of trading grain with the Phoenicians. With that trade cut off, Egypt's own economy would collapse. It's possible that Egypt would also grieve because the destruction of Tyre may mean that the Assyrians, if that's the attacker Isaiah has in mind, may soon turn its sights on them.