Identify the participle and the word the participle modifies. One day my friend, excited about her new bicycle, called me on the phone.

Participles have two forms - they either look like verbs + ing, or like past form of a verb (adding - ed to regular verbs, or third column of irregular verbs). They often function as either adjectives or adverbs in a sentence. So, having that in mind, the only participle in this sentence is the word excited, and it modifies the noun friend.

The friend was excited, which is why the latter word modifies the former.