Using a USB-C laptop charger to charge your phone is generally safe due to the USB Power Delivery (USB-PD) standard, which enables communication between charger and device before power transfer. The phone pulls only the power it needs, preventing overcharging or damage. This negotiation process ensures compatibility even with mismatched wattages.

While high-quality, recent chargers and devices (from the last decade) pose minimal risk, older devices, cheap accessories, or damaged cables may cause issues. Charging speed depends on the phone’s fast-charging capabilities—not just the charger’s wattage. Proprietary protocols from some brands may require specific accessories for optimal speeds.

Ultimately, USB-PD makes cross-device charging safe and practical for most modern smartphones and laptops.