Phillips screws? I doubt it. GM uses phillips trim scres, but those look like countersink type screws. If GM doesnt use a trim screw, they use a 9/32 headed screw, so no, I doubt those are iriginal
Aftermarket speakers, stock speaker screws.
Yes, those are what GM used to put the dash speakers in.
The stock speakers I pulled out had a black mesh type material over the top.