To install a Safari web extension on your iPhone, follow these simple steps:

• Open the Settings app on your iPhone.
• Scroll down and tap Safari.
• Tap Extensions.
• Tap "More Extensions" to open the App Store.
• Search for the specific web extension you want to install.
• Download the app that includes the extension.
• After downloading, go back to Settings > Safari > Extensions.
• Toggle on the extension you just installed to enable it.
• Once enabled, the Safari extension should be available for use while browsing on your iPhone.