Since Blocs uses the Bootstrap framework, the breakpoints are just the Bootstrap standards. The smaller breakpoints are still valid for phones. Don’t get lost in the pixels, because take for example the iPhone 6, which has a 1334-by-750-pixel resolution, but it is equivalent to 375px device-width size.
iPhone x has a resolution of 1125 x 2436 pixels, but the device width is 375px.
Some helpful info