Is it a sin to engage in cyber sex / phone sex?

from the old testament

• Humans were designed in God's image: "So God created man in his own image, in the image of God he created him; male and female he created them" (Genesis 1:27). Image-bearers should not participate in inappropriate sexual activity.
• God’s design is for sexual activity between a man and woman only in the context of marriage: "Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh" (Genesis 2:24). Cybersex violates that.

from the new testament

• Jesus explicitly repeated God’s design for sex and marriage: "So they are no longer two but one flesh. What therefore God has joined together, let not man separate" (Matthew 19:6). Cybersex is sexual activity outside of marriage.
• Deviations from God’s ideal for marriage and sex result in a variety of personal, family, and society concerns. In particular, the New Testament teaches believers to avoid lust and adultery, addressing both the desire and actions involved in sexual immorality (Matthew 5:27-28). It doesn’t matter that cybersex involves no touching. What matters is that it involves lustful thoughts and words between those who are unmarried, which is a violation of God’s design for sex.
• Believers are to keep their thoughts pure: "Finally, brothers, whatever is true, whatever is honorable, whatever is just, whatever is pure, whatever is lovely, whatever is commendable, if there is any excellence, if there is anything worthy of praise, think about these things" (Philippians 4:8). Cyber sex involves sexual thoughts, desires, and actions that displease God and are condemned as sinful in Scripture.
• Further, Hebrews 13:4 teaches, "Let marriage be held in honor among all, and let the marriage bed be undefiled, for God will judge the sexually immoral and adulterous." An "undefiled" marriage here includes avoiding adultery and other forms of sexual immorality. This could include any other forms of lust, pornography, sexual fantasies, and cyber sex. Christians should instead seek to honor God through thoughts and actions that please Him, help others, and support godly families.

implications for today

Engaging in cyber sex, sexting, or phone sex goes against God’s design for sexuality, which is meant to be expressed only within the covenant of marriage between one man and one woman (Genesis 2:24; Matthew 19:6). Even though it doesn’t involve physical contact, cybersex still cultivates lustful thoughts and desires, which Scripture condemns as sinful (Matthew 5:27-28). It distorts the sacredness of intimacy, replacing genuine connection with temptation and fantasy that harms both your heart and your relationships. Using your phone for sexual gratification can create habits that draw you away from God’s call to holiness and purity (Hebrews 13:4; Philippians 4:8). Setting firm boundaries—avoiding explicit messages, apps, or content—helps protect your mind, preserve your integrity, and honor God. Those who struggle with sexual addictions should not be viewed as "worse sinners" or beyond help. Instead, they should seek accountability from a trusted friend, mentor, or counselor to encourage and guide them to resist these temptations. By rejecting cyber sex, you choose to safeguard your heart, uphold God’s standards, and live your life according to His design for healthy, marital intimacy.