Do I need an actual mac to write iphone apps or can I just use a virtualbox or EC2

I have to write an iphone app. Can I do it if I just buy an iphone to run it and use a virtualbox install of macos and/or use an EC2 Mac Instance

https://aws.amazon.com/ec2/instance-...!!g!!mac%20aws

Or do it in a virtualbox?

Trying to avoid buying a mac.

thanks