why does my phone show extended instead of wifi

Do you mean when you go to Settings > WiFi, you see "Extended"?

Might that be the name of a nearby WiFi network?

If that is not what you mean, please explain what "WiFi section" means -- where exactly do you see "Extended"?

If you are seeing EXT after the carrier name at the top of the screen, it's using Extended Coverage

http://www.simplyconnect.ca/faq/extended-coverage-faq