During the physical development phase, which ability is developing in infants?

During the physical development phase, infants are primarily focused on developing gross motor skills. This encompasses the large movements that involve the coordination of arms, legs, and whole-body motions. Key milestones in this area include actions like rolling over, sitting up, crawling, and eventually walking. The development of gross motor skills is critical as it lays the foundation for more complex physical activities and ultimately contributes to a child's overall growth and independence.

While the other options may be important aspects of overall child development, they are not the primary focus during the initial physical development stage. Language skills, social interactions, and problem-solving abilities tend to emerge later as children grow and begin to engage more with their environment and peers. Thus, the emphasis during this early stage is primarily on those gross motor skills that enable infants to explore their surroundings and gain mobility.