Roll-top dry bags are the only real option.

Roll-top closures. That’s the feature you need.

Zippers let water in eventually, no matter how much they claim to be waterproof. Sand gets in the track, the seal degrades, and suddenly your phone is in a bag full of salt water. A roll-top dry bag is basically a sealed tube of rubber or coated nylon. You roll the top down three times, clip the buckle, and it’s genuinely waterproof — even if you drop it in the surf.

Don’t overthink this. You do not need a fancy “beach bag” with a waterproof lining. Those are marketing gimmicks. What you need is a dedicated dry bag, the kind kayakers use. They come in bright colors so you don’t lose them in the sand. They’re lightweight, pack flat, and cost $15–30 for a size that fits a phone, keys, wallet, and sunscreen. Get one with a D-ring if you want to clip it to your chair or towel.

Just make sure it’s actually a dry bag, not a “water-resistant” tote. If it doesn’t have a roll-top, keep walking.

Your phone doesn’t care about fashion at the beach. It cares about staying dry.