I didn't unpair my apple watch from my old iPhone and I erased my old iPhone and now it won't pair with my new one.

Or on the watch, go to setting>General>Reset select "Erase all content and Settings".

Unpair and erase your Apple Watch - Apple Support

i lost old phone and watch is linked to it so cannot get on apple watch to connect it to new phone

And read the section "if you don't have your old phone".