Mobile Display Error

Hello

BACKGROUND:
I’m trying to help my mom troubleshoot her website. I don’t really know anything about this stuff, but it appears to be trying to call a non-existent function. I’m not sure if the error message she’s being emailed is related to the mobile viewing problem either.

Help would be most appreciated. Times are tough right now and I really need help in getting this working for her. Please break down explanation like I’m 5 so I can walk her through it.

ISSUE:
Error when trying to load the page in mobile browser (Safari, Brave/Chrome, etc.)

ERROR MESSAGE:

Error Details
=============
An error of type E_ERROR was caused in line 74 of the file /var/www/wp-content/plugins/designthemes-core-features/custom-post-types/dt-portfolio-post-type.php. Error message: Uncaught Error: Call to undefined function spalab_cs_get_option() in /var/www/wp-content/plugins/designthemes-core-features/custom-post-types/dt-portfolio-post-type.php:74
Stack trace:
#0 /var/www/wp-content/plugins/designthemes-core-features/custom-post-types/dt-portfolio-post-type.php(52): DTPortfolioPostType->createPostType()
#1 /var/www/wp-includes/class-wp-hook.php(308): DTPortfolioPostType->dt_init('')
#2 /var/www/wp-includes/class-wp-hook.php(332): WP_Hook->apply_filters(NULL, Array)
#3 /var/www/wp-includes/plugin.php(517): WP_Hook->do_action(Array)
#4 /var/www/wp-settings.php(617): do_action('init')
#5 /var/www/wp-config.php(171): require_once('/var/www/wp-set...')
#6 /var/www/wp-load.php(50): require_once('/var/www/wp-con...')
#7 /var/www/wp-login.php(12): require('/var/www/wp-loa...')
#8 {main}
  thrown

The page I need help with: [log in to see the link]