What is the purpose of these forks?
They cross a line marked Primary / Secondary, so I assume they are a discharge path, to divert a lighting or static overvoltage so it doesn't burn through the insulation in the transformer. They're even labelled "SP1"

A discharge across the PCB may not necessarily be a disaster, while a discharge across the transformer will destroy it.

I think the lack of solder mask, and the round tips, are to try to make the breakdown voltage a bit more predictable. It will still depend on the air pressure and humidity.

Normally this would be done with a gas discharge tube, which has a much lower and more reliable striking voltage, but this might be too expensive in a phone charger.