Question

.Identify the participial phrase and the word it modifies.

Answer 1

The participial phrase in this example is 'running up the stairs', and it modifies, or refers to 'he', the person who is running and glancing. 

Answer 2

Running up the stairs, he glanced apprehensively behind him.

Participle phrase: running up the stairs.

Word modified: he.

A participle phrase will start with a present or past participle. If the participle is present, it will dependably end in ing. Likewise, a regular past participle will end in a consistent ed.

In this case the participle running is present because it ends in ing.

A participle phrase will tipically include objects and/or modifiers that complete the thought.