The county handles elections.
Philadelphia County and the City of Philadelphia are the exact same geographical area.
I don’t know how the governments separate themselves but I would assume the mayor in this situation would be aware of the staff numbers that will be opening and processing the mail in ballots.
Philadelphia is about 1.5 million people and I would assume thanks to Covid several hundred of thousands of ballots will need verified opened and counted likely by a staff nowhere near the size it should be because typical election does not have remotely that many mail in ballots.
Thanks. This is so bizarre. In Canada there is only one set of rules for the entire country in a Federal election and, yes, we require voters to show government issued photo ID. The same applies in most western countries. If there was no fraud President Trump would win 60-40.