Hi @extrinima, that might appear confusing, yes 
If they added up to 4 (eg: mdl-cell--2-col-phone, mdl-cell--1-col-phone, mdl-cell--1-col-phone) then the columns would all spread out across one row of the mobile screen. However, in this example, the first two columns (mdl-cell--2-col-phone, mdl-cell--2-col-phone) will fill up the row, so the next column (mdl-cell--4-col-phone) will clear them and be pushed underneath:
Anyway, the point is that yes, mobile viewports will behave as though there’s space for four columns.
Hope that helps!