On an iPhone, everything runs inside Safari — there's no App Store listing to search for and no update notifications to manage.
Add the page to your Home Screen (Share → Add to Home Screen) for quick access that looks and feels like a native app icon. iOS's own EQ setting under Music playback settings can double up with this tool's adjustments, so it's worth checking that's set to "Off" first.
Apple's App Store review process and sandboxing rules make it slow to ship small utility apps. A Safari-based tool sidesteps that entirely — the same page works the moment iOS gets a Safari update, with no separate app release required.