This new Yahoo! mail layout is so much less user-efficient than the old one because you have increased the amount of screen real estate for page layout elements, controls, and widgets by probably 25%. This is evident in the fewer items viewable in lists (= more scrolling ... very inefficient!) and the fact that attachment preview fonts are not about 50% smaller, so you have to enlarge and enlarge, and then the attachment runs off the visible frame reserved for content in this God-Aweful design.

If phone users are the only users you care about (and many of them are using apps, not the web portal anyway, to read their mail, then it's time actual laptop / desktop users have to go find another mail service provider.