Am I correct to assume that the hardware/device piece is similar to a Pineapple (https://hakshop.myshopify.com/products/wifi-pineapple)?

As I understand it, the device is like a WiFi Router looking for nearby clients broadcasting their MAC. Since phones have the ability of turning themselves into WiFi Hotspots, could a phone/app offer this same capability, or is it missing a hardware piece that lives in Density/Pineapple?