For a game like roulette, the online casinos will have a live dealer (or sometimes just a live wheel where the ball gets inserted automatically). All your bets are placed on your phone screen but the wheel spins in real life, and then the result is seamlessly digitized, so you're paid out immediately.
These games are hosted by real human dealers in real-time, streamed through high-quality video feeds, and allow players to interact with both the dealer and other players at the table. The dealers sit at live casino tables and are filmed playing the game in real-time by several powerful cameras.