Security is a valid concern, but if you stick to licensed platforms, you will be fine on your iPhone. I personally use Pin-up because they have a solid reputation and use high-level encryption for all data. You can
play there safely through your browser and you don't even need to download anything from the App Store. They are licensed by the Isle of Man which is a very strict regulator in the gambling world. When you sign up, they offer a massive 120% bonus and 250 free spins which is a great way to start. I have never had a single issue with my account or my personal information being leaked. The mobile version also has a "Pincoins" system where you get rewards just for being active on the site. You can use these coins to get more bonuses or even real cash later on. It is a very transparent system and they have 24/7 support if you ever get stuck.