Can I change the Viewport dimensions to one of the standard phone sizes?

Hi. The ‘Free/Selected Viewport’ mode is not viable when I resize it, so I need to develop on a standard phone size (e.g. iPhone X or Samsung S10. So I go to:

Editor Preferences → Level Editor → Play → Game Viewport Settings

, and change the New Viewport Resolution to my desired Samsung device.

But in order to test the game I have to run it on “Mobile Preview ES3.1 (PIE)” or “Standalone Game.” But these take long to launch, and I can no longer run quick tests in the standard Viewport.

Is there a way I can keep using the standard Viewport page, but change the Viewport dimensions to one of my target phone sizes?