Is merely speaking over the phone sufficient to take one's wife back after a revocable divorce, or is an explicit declaration of reconciliation required, especially if the husband only recently learned the rulings of revocable divorce?

Revocation (of divorce) occurs by an explicit verbal declaration indicating it, or by an ambiguous verbal declaration accompanied by the intention of revocation. Scholars differ regarding its occurrence through action without a verbal declaration. If there is no verbal declaration or action indicating revocation, and the waiting period ('iddah) has ended, then the wife has become irrevocably divorced with a minor separation (baynunah sughra), and a new contract is required to remarry her.