Scaling Video Results in very poor quality

[mhump]

I am fairly new to Premeire Elements 2018, and I am trying to edit a video that was shot on a phone in "Portrait" mode.  In portrait mode, the top third and bottom third are not important so I don't mind losing/cropping those areas. 

The issue I am facing is that when I scale the video up to put more focus on the middle third, the quality is very bad. 

The video is 1080x1920.  What I am finding is that when I initially set the Scaling setting, the quality is still pretty decent.  Obviously there is some degradation, but it is acceptable.   It is after I click the "Render" button that it becomes very poor.  This is the case with any amount of scaling - even a small amount.  After clicking "Render" it is unwatchable.

I am also familiar with the trick to fill the sides of the frame with a "blurred" copy of the video.  I would still like to scale up a little bit fill more of the frame with the subject.  Is there a way to increase the scale a bit, and still maintain decent image quality?

Thanks

-M

[Peru Bob · Accepted solution]

Don't scale more than 110%.

[Steve Grisetti]

Yep. Bob called it. If you're upscaling that 1080x1920 to 1920 wide, you're upscaling by over 175%. No way that's going to look good.

If somebody stuck you with 9:16 footage, here's the solution most broadcasters use:

Using portrait 9:16 phone video in a landscape 16:9 Premiere Elements project - YouTube

[Bill Sprague]

You slay me.  You always make it look so simple!