Is it necessary to seek forgiveness from someone whose phone was used in a sin?

This act does not involve the rights of others if one is authorized to use it. Sincere repentance, fulfilling its conditions between the doer and Allah Almighty, is sufficient for the doer. The phone must be used in a way that pleases Allah Almighty, not in a way that displeases Him; as Allah Almighty says: "And [remember] when your Lord proclaimed, 'If you are grateful, I will surely increase you [in favor]; but if you deny, indeed, My punishment is severe.'" [Ibrahim:7].