Identify the infinitive phrase and the subject of the infinitive in the sentence below.
to speak clearly is essential to being understood.
infinitive phrase:
being used as a(n)

Infinitive phrases starts with infinitives that is, “to” added by a simple verb and can be used as nouns, adjectives or adverbs. In the case of including a main clause in the sentence, infinitive phrase separates it with comma.   ‘

To speak clearly’ and ‘to being understood’ are used as an adverb because ‘to’ precedes to the word ‘speak’ which is a verb, an action word.  

Adverbs are words used in shifting or adding meaning of a verb, clause, adjective, or another adverb. They can be used if: firstly, a sentence contains a subject and a predicate. Secondly, when a subordinate conjunction is used and thirdly, if it answer the ‘adverbial questions’ – when, why, when and how. It is also further categorized to time, place, manner, degree, condition, concession and reason.