"My phone gets laggier the longer I use it" isn't one problem — it's three different problems sharing one name: the processor is overloaded, the system is throttling it, or storage can't make room. Clean without diagnosing and you're mostly wasting effort — and iOS gives "cleaner and booster" apps no soil to grow on.
This pillar is built around a troubleshooting framework:
- How each root cause presents — lag + heat, lag + battery percentage jumps, lag + storage running low: symptom combinations point to different causes
- The matching actions — check battery usage, check battery health, free up storage; and why restarting only works for one of them
- Background management — the whitelist setup for Background App Refresh and Location Services: cooler and more battery-friendly without new hardware
Start with the three-causes framework in Why Is My iPhone Laggy?, then do a background cleanup with Background App Refresh.