Ok last question (hopefully) ! two organisms are in the same phylum but not the same class. another pair of organisms are in the same genus. which pair has more in common? why?

 The "pair of organisms that are in the same genus" (have more in common than the) "pair of organisms that are in the same phylum but not the same class".

The reason is that the the "genus" is a more specialized sub-classification;  and those pair of organisms in the same "genus" are, by definition /classification; already in the same phylum, same class, and same order, and same family, (and the phylum, class, order, and family all come before the "genus").

The chemical bubbles