I don't think this is a traditional/phone format thing. It's a "webtoon and tapas have jpeg pixel limitations" thing. Changing the format of traditional page comics to a phone scroll shouldn't inherently pixelate your drawing, something's up.
As someone who posts traditional mainly because I can't be bothered to copy and paste each page to a scroll format (I could, but it would take 30mins each time and on tapas I actually post page by page so it's a moot point anyway), I don't think you have to change to scroll, but I can admit that my tradi format looks kind of ugly in scroll. My only saving grace is most of the time the pages are kind of separated with their borders.
However like I said, if you have your pages and you're copy pasting your vignettes to a seperate scroll document, the only reason they'd be pixelated is if your scroll format document is immediately in tapas size, like 700px wide or something, where your work page should be over 1200px wide just to be able to work on it. If you copy paste to a high res scroll format it shouldn't pixelate, and tapas and webtoon being what they are, you can't get around the slight pixelation that'll happen when you upload, it'll do the same for your tradi pages.
That's actually a selling-point of my comic book and my patreon and why I leave my comic up for free despite the book being out: my drawing style is very detailed and the print quality is so much better that you're paying to see the images in HD, on paper or on screen.