I'm hoping that this behavior will be changed in a later build. I found this frustrating, because it didn't let me have tiles in as many horizontal columns as I'd like. In build 10122, you can resize the height of the Start menu, but not the width. However, Microsoft made another change to Start menu behavior that made it worse, not better. That's a smart move, because it cleans up the Start menu by getting rid of the double-headed arrow, and it's not likely people will want to switch between full-size and smaller-size Start screens very often. (I haven't had a chance to see the phone version yet.) To change the size between a smaller and larger Start menu, you have to go to Settings / Personalization / Start and make the adjustment in the "Start behaviors" section. Instead, users with traditional PCs and laptops get the smaller-size Start menu by default, while those with tablets get the full-screen Start menu. There's no longer a double-headed arrow to switch between the full-screen Start menu and smaller-sized Start menu. However, in the newest build, 10122, that behavior has changed. The Start menu in Windows 10’s latest build. You could also make it larger or smaller by dragging the top or right side. You clicked a small double-headed arrow on the upper-right of the menu to grow it to take up the entire screen or shrink it back to its original size. In Build 10074, the menu was made easily resizable. Since the late January release, Microsoft has changed the menu several times.
Microsoft's decision to kill the Start menu in Windows 8 was one of the more controversial decisions the company ever made - so in Windows 10, the company decided to backtrack and build it back in.