Answer : to erase the boards
In the sentence " Mr. Hutton asked me to erase the boards", the infinitive phrase is "to erase the boards". An infinitive phrase comes in a very simple formula that is (to + the simple form of the verb) including the objects if there are any. Infinitive phrases are not only phrases but they can also serve as adjectives, adverbs and even nouns. Here are some examples of infinitive phrases.
My mother told to buy lean meat for lunch.
To be physically fit and attractive is my only wish this summer.
