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.
