Final answer:
The gerund phrase in the sentence 'The room was filled with beautiful singing' is 'beautiful singing'. This phrase is acting as the object of the preposition.
Step-by-step explanation:
In English, a gerund phrase will begin with a gerund, which is an -ing verb, serving as a noun in the sentence. In the sentence 'The room was filled with beautiful singing', the gerund phrase is 'beautiful singing'. This gerund phrase is acting as the object of the preposition 'with'. The gerund here is 'singing', and it is modified by the adjective 'beautiful'.
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