Scaling Video Results in very poor quality

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