What is this icon depicting a phone and Wi-Fi together? After I factory reset my Nokia 6, this icon appeared. I've never seen it before. What is this icon in the highlighted part?
This is WiFi calling icon or VoWiFi. Disabling that WiFi settings removed the icon as confirmed by OP

It is used for making voice calls over WiFi, similar to Volte ( more so when signal connectivity is poor). On some phones, it is slightly different with the solid triangle replaced by traditional WiFi icon as shown here