"swimming laps at the pool" is a Phrase.
Phrases are groups of words that contain no subject-verb component, while clauses have a subject and a verb, they can be dependant or independant, dependant clauses have a limited meaning and it depends on the rest of the sentence but you can understand a meaning out of it, and independant clauses can be standalone-sentences.
this sentence: "swimming laps at the pool" has no subject and verb and it gives no meaning other than adverbial.