Iphone footage best practice?

Working in premiere pro, using iphone video can be a dissapointment. I get a lot of artifacts, blockiness and general degeneration, compared with the original, especially when just looking at the iphone screen. I know for a fact that;
HDR is not easy to adapt and mix with normal REC 709-material.
The variable frame rate can be a real trap when, for instance, trying to make a solid and stable tracking of the material.

So maybe a round trip to Topaz Video AI can be a solution, to create a more robust videofile that can be edited and graded with no loss.

What models and settings works best?
Lets take it from basic HD-resolution and 30 fps in mov.-container.
Would be happy if someone has found out the optimal solution. And even better, using the latest version 5.