Learners and probationary drivers aren't allowed to make phone calls whilst driving because:

Distraction: Using a phone while driving, even with a hands-free device, is a significant distraction. It requires mental focus that should be dedicated to safe driving, potentially leading to accidents.

Legal Consequences: In many places, it's illegal for learners and probationary drivers to use a phone while driving. Violating this law can result in fines, points on your license, or even suspension of your license.

Lack of Experience: Learners and probationary drivers are still developing their driving skills. Adding the distraction of a phone call can make it even more difficult for them to react appropriately to unexpected situations on the road.

Safety: Ultimately, the prohibition is in place to ensure the safety of the driver, passengers, and other road users. It's essential to minimize distractions and focus on the road while driving.