There is every chance you will be dipped into the water at the beginning of your parascend, the four couples on my trip were, so it wouldn't be safe to take your phone. If you had a friend on the boat also they could take pictures of you.
The crew take pictures of everyone and you can buy all they take, around fifty they told me, given on a memory stick for €20 for one activity or €25 for two activities. My pictures were good, much better than I could have taken as they had a really good camera