The phrase "full submersion" means completely immersing or plunging into something, typically water. It refers to being completely immersed or submerged in a liquid, where no part of the object is sticking out. Full definition
Recent studies have shown that boiling, full submersion of cauliflower in water when cooking, is not the best cooking practice if you want to preserve key phytonutrients in this cruciferous vegetable. (whfoods.org)
This may possibly hint that the upcoming handset will be able to survive full submersion in water. (ibtimes.com)