The antonyms for the phrase, "buys one-way ticket" could be "buys round-trip ticket," "book return flight," or "purchase a return ticket." These antonyms suggest the purchase of a ticket that includes a return trip or a round-trip itinerary. While buying a one-way ticket suggests a single direction or a one-time travel plan, purchasing a round-trip ticket implies a more comprehensive travel itinerary that includes a return trip. Moreover, the purchase of a return ticket allows travelers to pace their journey while making provisions for an extended stay or a change of plans. Therefore, buying a return ticket is often a more practical and flexible option than buying a one-way ticket.