Since you're already doing the research and calculations in Safari on iPhone, here's a setup that keeps everything organized without needing a separate app:
For the actual calculation and results, Notes works well because you can create one dedicated note per scenario (e.g., "CRS - Base Case," "CRS - With PNP," "CRS - After Language Retest") and just type in your inputs and the resulting score breakdown as you go. Pin the folder or the individual notes to the top of the Notes app (swipe right on a note or folder, or long-press and choose Pin) so you can get back to them in one tap instead of searching. If you want structure, use bullet lists or a simple table-style layout inside the note for each category (age, education, language, work experience, spouse factors), so you can see at a glance which score changed between versions when you update inputs.
For the actual calculator itself, since you're doing it in Safari, add it to your Home Screen as a web app (open it in Safari, tap the Share icon, then "Add to Home Screen"). That gives you a one-tap icon that opens straight to the tool without digging through bookmarks or search history, and it behaves almost like a native app.
If you want to track multiple calculators or reference pages you're comparing (draw cutoffs, official IRCC score charts, etc.), Safari's Reading List (tap Share > Add to Reading List) is worth using specifically because it saves an offline copy, so you can review pages later even without a connection — better than regular bookmarks for research you're actively comparing side by side.
Lastly, if you want your CRS notes accessible on a Mac or iPad too, make sure Notes is syncing via iCloud (Settings > [your name] > iCloud > Notes), so any updates you make on iPhone show up everywhere else automatically.