Are all apps safe and secure to upload onto your iPhone

Yes. All apps must follow the App Store Review Guidelines and undergo a stringent review before they are uploaded. Also the way apps are designed for iOS are "sandboxed", meaning they are restricted from accessing files stored by other apps or make changes to the device. But you must watch out for certain apps that pose a scam, such as cleanup apps.

A word of caution ... Before downloading an app, check the reviews to see if there are any red flags. Also check this Using App Store forum. Each app has its own rules about free trials that are easily misunderstood. And Apple considers all purchases final.