Obfuscation of email and phone using JavaScript
First of all, ES2015+ onwards have template literals forw easier interpolation of string and data. For instance:

function fix_m_link(){
  var item1 = '@'
  var item2 = '.'
  var m_clear_text = `test${item1}example${item2}com`
  document.getElementById('m_link').innerHTML = `&lt;a href="mailto:${m_clear_text}"&gt;${m_clear_text}&lt;/a&gt;`
}


Also, JavaScript uses camel case for naming. So you might want to change fix_m_link and m_clear_text.

Putting code in one line makes it hard to read. If you have a build step, let a minifier do this. If the code is very short (like in your question), the extra kilobytes saved from omitted newlines is not worth making the code unreadable. Write code for humans to read.

Now if you really want to obscure your email, use a contact form instead. Some CMSes support this out of the box. And if your site is static, there are third-party services that allow you to embed a contact form. Most of them also support captchas, which will deter automated form submissions.