How can I fix my call speaker on the iPhone 7 Plus after screen replacement?

Hi. I got my iPhone 7 Plus screen replaced after it was broken but everything was still working fine. Everything still works fine except the call speaker, it's not working at all and there's a red dot at the top right of the screen. It appears to be inside the screen and shifts to white when you tilt the phone downwards. Please tell me what that red dot is and why am I seeing it also how I can fix my call speaker?

It sounds like the connectors/cables that link the screen & front assembly of the phone to the back have not been refitted properly or have been damaged.

I've seen reports of similar effects on the iphone 6.

Take it back to wherever it was "fixed" and insist they get it working as it should.