Is larger a verb

No. If one is to say "something is getting larger", getting would be the verb, not larger. The root term large as a verb would be enlarge.

No, it's a comparative adjective. Formed from the adjective large. To form comparative adjectives you add -ed to adjectives with one syllable or you use more for adjectives with two or more syllables.

big - bigger, large - larger

interesting - more interesting, complicated - more complicated.

Also you use than: larger than, more complicated than

Their house is larger than ours.

This test is more complicated than I thought.