Question

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

Answer 1

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

Answer 2

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.