This variable can be used to get (or to set) the previous x position of the instance within the game room physics world. This is the position of the instance within the physics world in the previous step to the current one.
phy_position_xprevious;
Real (single precision floating point value, or undefined if the instance is not physics enabled)
xx = phy_position_xprevious;
yy = phy_position_yprevious;
The above code stores the previous x and y position for the physics enabled instance in two variables.