This syntax file adds syntax/highlighting groups for PHP 8 attributes. I wrote this as an addition to the official Vim php syntax which lacks attributes.

Either copy the file keeping the directory structure to your .vim home directory or use a plugin manager.

Plug:

Plug 'dr0bz/php-attributes-syntax'

This syntax will introduce few new groups and link them to standard vim sytnax groups:

You probably want colors that are less intrusive. Since attributes a written in the comment place. You can just take your regular colors and make them darker. For ex. here is my color of Keyword:

#cc7833

Find your's:

hi Keyword

Then use your color picker to make it a bit darker:

#995924

hi phpAttributeKeyword guifg=#995924

Do this to all attribute groups mentioned above.

Good luck and happy coding in vim:)