What happens if you didnt purchase the phone yourself,it was a gift and you dont have proof of purchace other than the serial no. etc?

Water under the bridge at this point, but the person who gave you the phone did not follow instructions:

What to do before you sell, give away, or trade in your iPhone ...Official Apple Support › en-us

Now, you will need to get a hold of the person who gave you the phone to have them release the Activation Lock on the phone. They are the only one who can do this.

How to remove Activation Lock - Apple SupportOfficial Apple Support › en-us

You will need to talk to the person who gave you the phone. Your phone is locked to the previous owner (or to be precise, it is locked to the last person who activated it to their Apple ID). Only that person can help you here.