Why does Phil get so upset when Tony asks if it's okay to step in his trench?

Phil says: 'When you've just spent hours, or even days, carefully digging and cleaning a trench, the last thing you want is someone to come and plonk their dirty big boots all over it. You might have spent a long time preparing the surface of the trench and there might also be archaeology in there that could be damaged by people treading on it.'