Items in the tagspopular tagscloud module do not render correctly within the determined width of a module, in this case: sidebar right, means: tags may exceed the given width of the module and then will not be shown correctly on mobile devices.
In the module settings, the standard value for Minimum fontsize is set to 1em and Maximum font size to 2em.
You can set Maximum font size to maximum 1.2 or 1.2em to render correctly for a phone in portrait mode…
In addition in my clean installation the heders font sizes do not resize correctly for phones, so I needed to adjust the h1, h2 etc. manually to fit …