Final answer:
The 'taking-in phase', which occurs in the first few days post-delivery, is when discharge teaching about infant care is most likely to be effective for postpartum psychological adaptation.
Step-by-step explanation:
The phase of postpartum psychological adaptation in which discharge teaching regarding infant care is most likely to be successful is during the taking-in phase, which is the first few days post-delivery. During this period, the new mother is adjusting to the physiological changes, including healing and dealing with postpartum vaginal discharge such as lochia, and is often more receptive to learning about how to care for her well-being, as well as her infant's needs.
This is also when establishing a sense of trust is crucial, and responsive caregivers can provide a secure environment conducive for both the mother and newborn to adapt. Caregivers should focus on reassuring and educating new parents about the importance of the newborn's first breath, the closing of cardiac shunts, thermoregulation, and the establishment of intestinal flora, among other vital postnatal adjustments.