Final answer:
The verb in the sentence 'They got back to work' is a 'phrasal verb.' 'Got back' is the phrasal verb that indicates a return to an action or state, in this case, 'to work.'
Step-by-step explanation:
The lexical verb contained within the sentence 'They got back to work' is a phrasal verb. This classification of verb combines a basic verb with another word, often a preposition or an adverb, to create a verb with a new meaning. In this case 'got back' is the phrasal verb that indicates returning to something, in this context 'to work.'
It's important to note that in some cases, the addition of a preposition or adverb can turn the verb into a different type, such as a phrasal prepositional verb or prepositional verb. However, 'got back' in itself does not require another object to complete its meaning, thus it remains a phrasal verb.