A gerund phrase is a group of words comprising a gerund.

• Running in the afternoon sun is so tiring.
• The gerund phrase: "Running in the afternoon sun"

• gerund	prepositional phrase
  Running	in the afternoon sun

Note that the gerund phrase functions as the subject of the sentence.

• I hope you appreciate my offering him this opportunity.
• The gerund phrase: "my offering him this opportunity"

• possessive pronoun	gerund	indirect object of action	direct object of action
  my	offering	him	this opportunity

Note that the gerund phrase functions as the direct object of the verb "appreciate".

• You might get into trouble for forging a medical certificate.
• The gerund phrase: "forging a medical certificate"

• gerund	direct object of action
  forging	a medical certificate

Note that the gerund phrase functions as the object of the preposition "for".

We have seen that gerund phrases can have multiple functions in a sentence. So be careful the next time you use it.