The volume change will be 30 mL.
The question appears to assume that all substances are present as gases, so let's proceed on that basis.
Step 1. Write the balanced chemical equation
Step 2. Calculate the starting and final volumes.
According to Gay-Lussac's Law of Combining Volumes, 1 mL of phenol reacts with 7 mL of oxygen to form 6 mL of carbon dioxide and 3 mL of water.
So, 30 mL of phenol reacts with 210 mL of oxygen to form 180 mL of carbon dioxide and 90 mL of water.
You are starting with 240 mL of reactants and forming 270 mL of products.
Step 3. Calculate the volume change