@Marshall
I'm with you, no smartphone, work from home.
keep as much as possible above the fold
The concept of fold doesn't exist in the mobile world. The user will often start scrolling a page before the ATF content has finished loading (specially ads).
a site tries to cram too much in a small space
With the mobile first index coming, taking the KISS approach (I interpret this as a stripped down view) may not be best approach. I think content presentation is one the most important aspects of mobile page design. The key is to present the content such that it is all there, but that it is not crammed and that it is easily scrollable/accessible.
Unfortunately, using tabs and other UI tricks to improve human readability is sub-optimal from Google's perspective. As tabbed and hidden content is devalued by Google's algo. I understand their logic for doing this, but I strongly disagree. For example, on my pages I use a lot of graphs. Users want to see the graphs, they don't immediately care about the underlying numbers. After some time reviewing the graph they may want the added detail of the numbers. So I tab the content top tab, graph, hidden tab table with numbers. Google now crawls the pages, sees the graph's but does nothing with them (as they are <svg>) and then devalues the hidden content, the numbers, which are in fact a means of describing the graph and should allow Google to interpret the content. The alternative is to simply present the all the content in a flat structure, but then you end with a page that scrolls and scrolls and scrolls.
I use via internet connection to test my designs
I simply use the emulator built into Chrome/Firefox. It is not like you can have a phone for each screen size. I do rely on friends and family, to double check for browser compatibilities.