why my phone cannot connect to the Apple Watch

What model of watch is it and what version of WatchOS is it running?.

What troubleshooting steps have you tried?.

What errror messages are you receiving?.

Has this watch ever been paired to another phone?

Start here;

Set up and pair your Apple Watch with iPhone

Going by that image it looks possible that your camera lens on your phone is smudged - this might affect its ability to scan the image on the Apple Watch. Buff the camera lens with a clean cloth and try again. Also ensure you have fully updated your iPhone's software.