What is the ruling concerning a husband who divorced his wife with a Sharia-compliant and court-sanctioned divorce, then returned to her with a Sharia-compliant contract, then divorced her for a second time and took her back before the expiration of her waiting period, then divorced her for a third time over the phone?

If the wife is taken back in the presence of her guardian and two just witnesses, and with a clear contractual صيغة (formulation) that indicates marriage and immediate acceptance, then the contract is valid, and it is not a condition for it to be in court. Based on what you mentioned regarding the presence of the guardian and witnesses, if you have divorced your wife twice after reconciliation, in addition to the first divorce, then she becomes unlawful for you until she marries another husband with a marriage of desire and he divorces her after consummation. Regret does not prevent the occurrence of divorce.