A Specific Absorption Rate (SAR) of 5.2 W/kg technically does exceed limits and device manufacturers agree to meet regulations. However, SAR values are not constant and can vary with real-world usage. Phones often operate at lower power levels, reducing actual SAR exposure.
A weak microwave, for theoretical comparison, would likely put out hundreds of Watts per kg.
People are way more likely to get heat damage from the battery than the radio waves from a cellphone