I’ve been doing that for years now on the iPad, and knowing Apple (my site’s 20+ years old, BTW), I would be extremely surprised if they ever put Stage Manager or anything similar on an iPhone. You can hack your way around things (Blink and Remote Desktop support external displays, etc., and there has been an external display API for a while that third-party apps have used creatively), but it is just not the way Apple thinks about the iPhone.
I’ve been doing that for years now on the iPad, and knowing Apple (my site’s 20+ years old, BTW), I would be extremely surprised if they ever put Stage Manager or anything similar on an iPhone. You can hack your way around things (Blink and Remote Desktop support external displays, etc., and there has been an external display API for a while that third-party apps have used creatively), but it is just not the way Apple thinks about the iPhone.