If two organisms are in the same phylum, which other classification category must they also share?

The correct answer is kingdom.

Explanation:

The hierarchy system used for the classification of the organism is termed as the taxonomic ranking. in this ranking, domains are divided in kingdoms, kingdoms are divided in phylum. The phyla are divided in class. The class is divided in orders. The order is divided in families. The families are divided in genus and the genus is divided in species.

The phylum is categorized as lower to the kingdom and higher to the class. So, organism belonging to same phylum must have the same kingdom.  

humans, along with other animals and plants, have linear chromosomes that are arranged in pairs within the nucleus of the cell. the only human cells that do not contain pairs of chromosomes are reproductive cells, or gametes, which carry just one copy of each chromosome.