I've been caught in 2 torrential downpours in the last month and my unzip- locked phone was fine. So was DH's I phone.
It's all personal preference, but I don't mind stuffing my jersey pockets or my seat bag, which is not huge, but bigger than the average roadie's. I would have a bigger bag if my bike could handle it, or at least a bigger one I could use for the occasions that warranted one. I have been slightly annoyed at some of the group rides I have done (this is a purely social group with good riders who always include a lunch stop) when we stopped someplace to get food and then actually had to carry it to a different location to eat, like a park. Well, there I was with a huge paper bag full of a sandwich and drink, it was 90 degrees out and we were on Cape Cod in summer traffic. I had to ask someone to carry for me and I felt terrible. If they had warned me, I would have worn my Camelbak.