What grammatical structure is the italicized portion of the sentence? put the sizes on the uniforms while sorting them out. adverb clause infinitive phrase past participial phrase elliptical clause adjective clause- -while sorting them out

The grammatical structure of the italicized portion of the sentence is an adverb clause. First option is correct.

To begin with, it answers the question "when?" It is a temporal phrase.

An adverb clause is a group of words that play the role of  an adverb in a sentence. Adverb clauses can be employed to add explanatory detail to a sentence or writing and explain how or why things happen.

Adverbs tend to answer questions such as, how, why, where and when.

they are most likely about to fight in the battle of gaul