Best waterproof snorkerling bags or fanny packs
Not a big Ziplock fan. Because of a tiny hole in a corner of a Ziplock bag, I lost an iPhone. I now lock a dry paper towel in my dry bag and submerge it in water overnight. If the towel is dry the next day, chances are the bag will keep things dry -- but I will not take a phone in the water again.
I would suggest looking at Amazon, dive shops, sporting goods stores, etc.. I have bought one in a sporting goods store in Iowa and one on Amazon (can't remember the brand, but there are dozens to choose from) and they both work. I have bought one in a FL kayak shop and it leaked. Just look for one that has a tight seal at the top (would not suggest the Ziplock-type closure) - and then test with a paper towel before you use it. If you are going to take your phone in a dry bag, be sure your phone is insured!!