I'm assuming this would be a companion product to the waterproofing service some third party providers offer. Otherwise you save a dead phone.
Anyway, the difficulty is the weight/density of the phone. In order to float the life jacket would have to either be rather big or inflate. To inflate that would likely require compressed air, which adds more complications - e.g. Taking your phone on a plane,
Not a bad idea. I just think the practical aspects will prohibit its implementation.
Also not really the business Koodo is jn. Koodo is a service provider, other than that they are a marketing machine. Third parties create and market cases and there are some that are "waterproof " but who knows.