An example of a parenthetical phrase would be the following: "The three boys (Bob, James and Joey) went out to get some ice cream. A parenthetical phrase can use either parentheses, commas, dashes or brackets to include nonessential information.
Parenthetical phrases are used to add information to a sentence that is not vitally important, yet it may be considered add some specific information. A parenthetical phrase can either be one word or many, but the phrase needs to be set off with punctuation. Any form of punctuation can be used to create a parenthetical phrase so long as there is a break in the sentence.