What should a husband do with his wife who sent scandalous pictures to a foreign man over the phone, considering her determination to repent and the presence of three children between them?

If the wife engaged in a phone relationship with a non-mahram man and sent him her pictures, she has disobeyed her Lord and fallen short in her husband's rights. She must offer sincere repentance. If her repentance is truthful and her conduct improves, then hold onto her and treat her kindly. Be keen on protecting her and nurturing her in faith by connecting her with Quran memorization circles, faith gatherings, and the company of righteous women. However, if you strongly suspect that she is not sincere in her repentance, then divorcing her is better. As Ibn Qudamah mentioned, divorce is recommended when a woman neglects her obligatory duties towards Allah or if she is not chaste.