Is this an example of a participial phrase?

The man in the suit was her former fiance.

No. Your sentence doesn't contain a participial phrase.

Check this site for information about participial phrases.

http://grammar.uoregon.edu/phrases/participialP.html

I didn't write it. It was on a worksheet. But I do have to fix it. I already went to that site and if I were to change it to:

The man wearing the suit was her former fiance.

would that make it a participial phrase?

Yes. The participial phrase is "wearing the suit," and it modifies "man."

Thank you!

You're welcome.

Yes, "The man in the suit" is an example of a participial phrase in this sentence. A participial phrase is a group of words consisting of a present or past participle form of a verb and any accompanying modifiers or objects. In this case, the present participle form of the verb is "in," which functions as an adjective modifying the noun "man." The phrase describes the man's appearance, indicating that he is wearing a suit.