You seem to be misunderstanding something. All verbs have both standard form and polite form. 食べられます is the polite form of 食べられる. It's totally the same as the polite form 食べます vs. plain form 食べる.
It's explained in the site, no?
But the entire point of using keigo is to confer respect and be polite to your listener and so using the standard form of the verb defeats the entire purpose. Consequently, everything gets put in the "polite form" (teineigo).
Also, ✘ clearly shows that 部長、お客さんに電話されるの? is wrong.