Is the marriage of the questioner to a girl he met online and then by phone, which was conducted in accordance with Sharia, permissible in Islamic law, and what is the ruling on the child born from this marriage?

Familiarity between marriageable men and women and the love relationship between them—even if for the purpose of marriage—is a door to temptation, a means to corruption, and evil.

However, since you married this woman with a valid Islamic marriage, your marriage is sound and there is no objection to it, and your child from her is undoubtedly attributed to you.

Divorce might be better, as Allah Almighty says: (But if they separate [by divorce], Allah will enrich each of them from His abundance) [An-Nisa: 130].