What to replace mysqli_fetch_fields in PostgreSQL?

As far as I know, there is no direct counterpart.

Vskidku, you can try to do this (the part in the full list there are a number of functions):

• pg_field_num - php.net/manual/ru/function.pg-field-num.php
  
• pg_field_name - php.net/manual/ru/function.pg-field-name.php
  
• pg_field_table - php.net/manual/ru/function.pg-field-table.php
  

Full list:
\rphp.net/manual/ru/ref.pgsql.php