Having completed his chores, he settled into his favorite armchair to read a book. Here the underlined part is a/an -

♦ Having completed his chores, he settled into his favorite armchair to read a book. Here the underlined part is a - Participle phrase.

• যে phrase, participle দিয়ে শুরু হয় এবং noun দিয়ে শেষ হয়, তাকে participle phrase বলে।
- Participle phrase মূলত sentence এ adjective এর মতো কাজ করে।
- Participle Phrase + Comma + Whole Sentence

• প্রশ্নে উল্লেখিত বাক্যটির গঠন - 
- Perfect Participle + Noun (chores) + Whole Sentence এবং
- অর্থাৎ, phrase টি participle দিয়ে শুরু এবং noun (chores) দিয়ে শেষ। 
- তাই এটি Participle phrase.