Depending on your bank you might need a Swedish phone number, but you actually don't need a phone to receive money. (In reality the phone number has nothing to do with it, it's just a pre-existing ID)

You need the app to be able to send money though (iOS, android or windows phone).

Yes it is stupid. Unfortunately it is convenient, which is enough for 95% of the population.

To a degree. A bigger issue would actually be BankID, which is the secure online authentication service in Sweden, used by banks, government, insurance companies, etc.

But there are still, somehow, banks in Sweden which don't support one or the other. And, well, useful as Swish is, it's not actually obligatory for life in Sweden.

For what it's worth, BankID and Swish also support Windows Phone… for the remainder of 2018, anyway.