You have to declare all of your debt. Whether you can keep a mobile phone contract will depend on the OR and whether or not the company will let you keep it.
I suggest you speak to an expert. There are a couple who post on here and whose details can be found under the expert link on the left hand side of the page. The advice is free.
The friend in my adversity I shall always cherish most. I can better trust those who helped to relieve the gloom of my dark hours than those who are so ready to enjoy with me the sunshine of my prosperity. – Ulysses S. Grant
You are allowed to have some creature comforts, I was allowed to keep my contract phone but I chose not to.. (fresh start N all, so many options life giffgaff which is contract service with PAYG prices)
You must declare it like Niobe says. if you don't the OR can get funny with you and last think you want is a long marker on you for not playing ball.