Rerun phrases always end in - ing and are used as?

If it ends in - ing, it is used as a present tense.

I believe you mean to say 'gerund' phrases, not rerun phrases - there is no such term in grammar.

Anyway, gerund phrases look like verbs - they are formed by adding - ing to the verb itself (sleeping, drinking, eating, etc.). However, they are not used as verbs - they are used as nouns in a sentence. For example:

Sleeping is good for you.