There is currently no official, maintained SelfControl app for iPhone. The SelfControl team's own FAQ gives two specific reasons: iOS's sandboxing doesn't allow the system-level hosts-file and firewall access the Mac app depends on, and Apple's App Store doesn't accept GPL-licensed code, which is how SelfControl is licensed. An early iOS prototype does exist in the project's GitHub, but it was never finished or released and hasn't been touched since 2017 — so this isn't a settled technical impossibility so much as a project the maintainers chose not to pursue.
A useful self-control app for iPhone does more than show a report. It helps at the moment you usually open Instagram, TikTok, YouTube, Reddit, or another distracting app without intending to.
Start with Apple Screen Time. It provides App Limits, Downtime, and activity reports. That is enough when a reminder or time budget changes your behavior.
Use stronger friction only when the light option fails. A pause can interrupt a reflex. A default block is more appropriate when you keep ignoring limits, reopening social media during study or work, or need an app installed but not freely available.