Phenolic foam is extensively utilized as a thermal insulation material, and its performance is significantly affected by the ingress of external rainwater. To simulate the material’s environment, we conducted indoor tests to assess its water absorption characteristics under varying water pressure heads. Additionally, we utilized CT scanning to analyze the distribution of water within its pores. The findings indicate that the specimens’ water absorption patterns are quite consistent across different water pressures, with a maximum absorption rate reaching approximately 3200% after reaching a basic level of stabilization. For the novel water-absorbing phenolic material, we processed the CT scan images to enhance clarity and established criteria for determining the gray levels of pore water. It was observed that the phenolic material’s water-absorbing infiltration interface was relatively flat, with localized high infiltration heights at points where large pores interconnected, forming water columns. Microstructural analysis was conducted to elucidate the mechanisms behind the formation of these prominent water columns.