There isn't a true homophone in the sense of a word with the same pronunciation but different spelling and meaning. "Urge on" is already a phrasal verb.
However, there are words that sound similar and could be confused, like:
* "urge" - This is the verb form of "urge on."
* "urge forward" - This is a similar phrase meaning to encourage someone or something to move ahead.
It's important to consider the context of the sentence to determine the intended meaning.