get blog page url in WordPress

You can use get_option of page_for_posts to get the page ID to either assign it to a variable or to echo it.

<?php echo get_permalink( get_option( 'page_for_posts' ) ); ?>

For more information of the default get_option visit: Option Reference

We can use get_post_type_archive_link since WordPress 4.5

get_post_type_archive_link( 'post' );