Question: "Is cyber sex / phone sex a sin?"
Answer: The Bible nowhere mentions cyber sex or phone sex, obviously, because "cyber-anything" and "phone-anything" were not possible in Bible times. The Word of God does give us some principles that apply to activities such as cyber sex and phone sex. Philippians 4:8 tells us, “Finally, brothers, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable—if anything is excellent or praiseworthy—think about such things.”
There are many Scriptures which indicate that sex outside of marriage is a sin (Acts 15:20; Romans 1:29; 1 Corinthians 5:1; 6:13,18; 7:2; 10:8; 2 Corinthians 12:21; Galatians 5:19; Ephesians 5:3; Colossians 3:5; 1 Thessalonians 4:3; Jude 7). Jesus Himself taught us that to desire something that is sinful is also sinful: “You have heard that it was said, 'Do not commit adultery.' But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart” (Matthew 5:27-28). Proverbs 23:7 says, “For as he thinks within himself, so he is.”
Cyber sex and phone sex are, in essence, desiring something that is sinful (fornication or adultery). Cyber sex and phone sex are fantasizing about that which is immoral and impure. In no sense could cyber sex or phone sex be considered noble, right, pure, lovely, admirable, excellent, or praiseworthy. Cyber sex and phone sex are virtual adultery. They are fantasizing about a person lustfully and encouraging another person into immoral lust. They lead a person into the trap of “ever-increasing wickedness” (Romans 6:19). A person who is immoral in his/her mind and desires will eventually become immoral in his/her actions. Yes, cyber sex and phone sex are most definitely sins!