Im wondering what is the diff between using the rc to control the mavic and using the smartphone to control the mavic via wifi

Hi. Thank you for raising this question to us. The Mavic remote controller uses DJI’s OcuSync transmission technology, giving it an increased range of up to 4.3mi (7km) in open areas without interference, FCC compliant. When using a smartphone connected via Wi-Fi, the controllable range is 80m, and maximum altitude is 50m, making it suitable for short-range shots like selfies and for setting up ActiveTrack. You can also download photos and videos directly from the Mavic to your mobile device via Wi-Fi. By sliding the Control Mode switch on the right-hand side of the aircraft, you can choose easily between Wi-FI and RC mode depending on which transmission type you need.

About 6,920m in range Use the RC.

It always helps to read the manual too...