Engadget
How to use your old Android phone as a Wi-Fi extender

An Android phone can become a Wi-Fi extender by connecting to the home network, then enabling the Wi-Fi Hotspot in Settings, renaming the SSID, setting a password, and optionally choosing 5 GHz. Place the device midway between router and dead zone; it rebroadcasts the existing signal without increasing speed or offering smart-home integration.