i agree with the slide leg getting out of the way. But, the ball is getting to the foul line before you finish your slide.
It looks like your back swing could be higher ,getting your backswing higher will delay when the ball get to the release point and you should be able to get your trail leg out of the way.
read this http://www.bowl4fun.com/ron/tip33.htm
4.) Cutting off the backswing: A lot of bowlers unknowingly cut off their backswings. This means that they stop the ball from reaching its full height in the backswing. Bowlers subconsciously think they have to “throw” the ball. They get in a hurry and cut off the backswing in order to “throw” it forward. It is far better to allow the ball to reach its full height in the backswing and allow gravity to turn it around and pull it back down toward the earth and the lane.
A good way to test to see if your backswing can go higher ,or if it needs to, is to have a friend stand beside you as you bowl and note how high your backswing goes. If your backswing does not go at least as high as your head, try to raise it. Standing still doing test swings have your friend hold his hand palm side down about 1 foot higher than your normal backswing height and see if you can “will” the ball to go up and hit the hand. Most people can raise their backswings using this method with no additional effort on their part. If you apply numbers 1-3 to your armswing, the task will become even easier. Once you can hit your friend’s hand when you are standing still, have him walk along beside you as you bowl and hit his hand again. It may seem like it takes forever for that ball to go up there and hit that hand, but this is just because you are used to stopping the ball short and forcing it.