How do I set my canvas / camera to represent what will be put on phone screen?

I would like to have my computer screen reflect better what will be seen on my phone. I have the aspect ratio set on my computer and am using UI buttons.

Currently, I size my buttons and place them on my computer in a way which I think looks right. Then when I test it out with the unity remote, the buttons are WAY smaller and too close to the edge of the screen.

I figure someone out there must have a setup where their computer reflects much better what will be put on the phone. Any ideas?