If you can connect from any other system via FTP and internet (WAN), it is not the destination then. Destination does not care what hardware you are using, as long as you are using FTP protocol.
So double check and compare the FTP settings between the Iphone and Win PC. Try by IP vs DNS, make sure credentials are correct, etc etc.
And last, FYI… FTP is NOT a SECURE protocol. Of course, only if you require security or care about it. For more info, search this forum.
