Phia, a soon-to-launch fashion platform, partnered with Stella McCartney to design a new bag collection that honors the Women’s Tennis Association and 50 years of women being paid equally in tennis.

Sophia Kianni and Phoebe Gates, two Stanford undergraduate students and activists, see room for improvement in the fashion industry. As leaders in advocacy for environmental awareness and women’s rights—Kianni is a United Nations advisor and the founder of Climate Cardinals, a youth-led nonprofit focused on making the climate movement more accessible, and Gates is a reproductive rights activist—the pair was surprised to find that after being randomly matched as roommates, they had a lot in common. “It felt like such a star-aligning moment; we barely knew each other the year before,” Kianni says. Now, they’re combining their respective backgrounds to launch their first business, Phia.

It comes as no suprise, given their shared passion for making a difference, that Kianni and Gates are embarking upon a venture with a cause. Phia, a digital fashion platform, is set to launch this fall. While the product itself is still baking, the co-founders set themselves up for success by tapping a mentor and conscious fashion pioneer: Stella McCartney. “We’re trying to build something that we think will change the future of fashion,” Kianni says. Gates adds, “Stella has been able to build this empire while still holding onto her values. We reached out many times, and eventually, she really took us under her wing and has since been an advisor to us as we build out this platform.”

In anticipation of Phia’s launch, Stella McCartney and Phia came together to celebrate the 50th anniversary of the US Open, becoming the first Grand Slam tournament to offer equal prize money for women. Gates and Kianni collaborated with McCartney to design a limited-edition capsule collection of bags that honors this advancement for the Women’s Tennis Association. McCartney’s past partnerships with female tennis players, such as Maria Kirilenko and Caroline Wozniacki, and, of course, Adidas, have tied her closely to the WTA and its mission of empowering girls and women worldwide.

The bag, which is available in two slightly different iterations, is designed with chain handles and crystal-embellished ribbons as a nod to a powerful feminist accessory in sports history, the tennis bracelet. “Chris Evert, 50 years ago, dropped her diamond tennis bracelet on the court. And it was this whole thing where she stopped the game to pick up her bracelet,” Gates says. “So the bag we designed, which is made from deadstock materials and inspired by that story, is designed to support women in tennis and honor these 50 years.”

While Gates and Kianni make it clear that they’re not athletes themselves—“as you can see from the way we’re dressed right now,” Gates jokes—they are following the path female tennis players have long paved to make changes for future generations. “Both of our backgrounds, all of it has been about bringing people from grass-roots activism to philanthropy together,” Kianni says. “That’s very much the same spirit we want to honor as we enter the fashion space. We want to identify everyone who is doing incredible things, learn from them, and see how we can accelerate progress together.”

To celebrate the launch of the collection, Gates and Kianni filled the Stella McCartney Greene Street store with friends and family. Champagne and Casa Dragones cocktails poured as partygoers got a first look at the co-designed bag, a light-pink take on a quintessentially Stella McCartney design. As the co-founders look beyond this milestone partnership, they have one shared goal in mind. “I’m just inspired to work with women who I think are so incredible—I get to work with Sophia every day,” Gates shares. Kianni echoes her sentiment, “At this party is everyone from every walk of life — some of our mentors have come, our friends from school are here. It’s really important to foster intergenerational collaboration. Because I think there’s a lot we can all learn from each other.”