Red dot not orange appearing when I make or answer a call.

https://support.apple.com/en-ca/HT207354 provides details on the rest of the status indicators you'd see on your phone's status bar.

If nothing in here looks like what you see, it's probably specific to an app you installed on the phone, or it's part of your device's background wallpaper (if it appears all the time, which it doesn't sound like is happening--just thought I'd thrown it out there for good measure).

Are you sure it's red?

https://support.apple.com/en-us/HT211876

The dot will appear red or orange depending on the background and display settings. Regardless, it means the microphone is in use.