I think that the quality of the film isn't bad at all for an iPhone!!
Your horse is lovely and I bet his canter is really comfortable to sit to!
He obviously knows his job, and I think that you have a good position.
Just a couple of things that I would suggest if you were my student:
* you seem to lose impulsion during turns. This happens to a lot of people. Your horse is big and you need to try to encourage him to keep the cadence and impulsion so that each jump is approached correctly and the action smooth.
* You got caught out at the last jump - but well sat! Often, us show jumpers seem to forget that only the horse jumps, not us! Just wait for the jump to come. Sit quietly, leg on, guide your horse and let him get on with it. At that height he will work out the strides for himself, you don't have to worry about it!
As I said before, the horse knows what he's doing and you did a great job!!