Hello  @Pinkesh 

RE copies the SSID from router if you used WPS button or chosen' copy host SSID 'during set up.
Please change a different SSID / WiFi name for range extender and see phone and PC or cell phone could see RE's Wi-Fi?

(via Tether APP)How to change wireless settings of TP-Link range extender on Tether APP

(via Web GUI) How to find or change the wireless settings of TP-Link Range Extender

Or you could factory reset range extender and set it up through web page or Tether APP, and create RE's own SSID during set up process.