Can't login to mysql as root user even though I have the password

I followed this tutorial on how to set up phpMyAdmin on Ubuntu 18.04: https://www.digitalocean.com/community/tutorials/how-to-install-and-secure-phpmyadmin-on-ubuntu-18-04

In step 2 I’m trying to log in to mysql using the command sudo mysql but I get the error message Access denied for user ‘root’@‘localhost’ (using password: NO)

I’ve also tried logging in with the root user using the root_mysql_pass located in /root/.digitalocean_password but I get the error message Access denied for user ‘root’@‘localhost’ (using password: YES)

I’m able to log in as the user wordpress with the password wordpress_mysql_pass.

Does anyone know what’s causing this or how to solve it? Any help I can get is very much appreciated!