What should a girl do who met a young man online and talks to him on the phone, and feels deep regret and distress?

You have transgressed the Sharia (definition) and fallen into what Allah has forbidden by establishing a relationship with a young man. It is obligatory upon you to cut off the relationship immediately, change your phone numbers, stop appearing on chat programs, and repent to Allah with sincere repentance before it is too late. Your feeling of regret and tightness in your chest after the phone call is evidence of the remaining purity and chastity within you, and that your faith forbids you from continuing the sinful relationship. "Whoever is bothered by his evil deed and pleased by his good deed is a believer." Ask Allah to grant you chastity and a righteous husband, and associate with righteous companions who will help you remain steadfast. Listen to beneficial religious tapes such as "Sincere Repentance," "And beware of a Day when you will be returned to Allah," "A Session on the Sidewalk," and "On the Path."