Strip html tags in preprocess hook

We have a mytheme.theme file that has a mytheme_preprocess_node(&$ variables) function. Within this preprocess hook, we would like to remove all HTML tags within a formatted (long) field. The goal is to do without using striptags within the node--page.html.twig template.

How can we do this securely without using striptags in a twig template?

Here is what we tried, but cannot find how to do it using mytheme_preprocess_node hook.

mytheme.theme

function mytheme_preprocess_node(&$  variables) {    $  node = $  variables['node'];   $  field_value = $  node->get('body')->first()->getValue()['value'];   ksm($  field_value);   // cannot find way to remove `html` tags } 

output of ksm($ field_value)

"& lt;p & gt;When looking at & lt;a href="https://www.example.com/some-path/"& gt;article trends& lt;/a& gt; over time, attacks are cyclical in nature. Attackers develop new attack types and vectors, which are used to launch a new wave of attacks. As defenders become more proficient in stopping these new attacks, the attackers develop new types of attacks and the cycle repeats itself.</p& gt; 

In order to properly display the output, I had to a space between & and lt characters above because StackExchange will convert those to proper tags. Within the ksm statement there is no space.