The children playedin front ofthe house, building a sandcastle in the driveway. Here the underlined phrase is a/an -

♦ The children played in front of the house, building a sandcastle in the driveway. Here the underlined phrase is a - Phrase preposition.

• Phrase preposition: 
- কয়েকটি word গুচ্ছগতভাবে Preposition এর কাজ করে।
- Phrase preposition এর শুরুতে এবং শেষে preposition থাকে।
- যেমন - in front of, because of, according to ইত্যাদি।

সে অনুসারে, in front of হচ্ছে Phrase preposition.

• Prepositional Phrase:
- যে Phrase – Preposition দিয়ে শুরু হয়, কিন্তু Adjective বা Adverb এর কাজ করে, তাকে Prepositional Phrase বলে।
- A prepositional phrase consists of a preposition followed by its object (usually a noun phrase).
Example: A singer with passion.
- Prepositional phrases function as either adjective-modifying nouns or adverbs-modifying verbs.
As an adjective: I know the policeman with the radio.
As an adverb: Lee lives in that fridge. (These types of prepositional phrases are adverbial prepositions)

Source: Advanced Learner's by Chowdhury & Hossain.