If you have sufficient layover time, you could take the Green Line train from the airport to the Apple Store at the downtown City Creek mall (but closed on Sundays). Get off at the City Center Station and you are right there. Trains generally depart the airport every 15 minutes and it is about a 20 minute trip (versus about 15 minute trip if you take Uber).

From their website https://www.apple.com/retail/citycreekcenter/ it looks like you can order the phone ahead of time so that it is ready for you to pick up when you arrive.