There is no foul slider. However, User and CPU line sliders greatly affect player positioning. And players that are in closer proximity to each other on the pitch have a much greater chance of interacting, which by default will lead to more fouls. Below are two examples using the same teams and same settings, other than line height and line length slider settings. In fact, all I did was pause the game and switch the two line sliders, and this is the result from one moment to the next.
You can see from the player positioning in screenshot #2 that players will naturally have a much greater chance of fouling each other as they fight for ball possession. Plus the positioning of both teams is much more realistic, whereas player positioning in default FIFA looks much closer to screenshot #1. One can easily see and understand why fewer fouls would happen with the default game settings: