Background/Objectives: PHF6 is a chromatin-binding protein located in the nucleus, and it is involved in transcriptional regulation. However, limited research exists on the specific roles and mechanisms of PHF6 across various tumors. Methods: Based on The Cancer Genome Atlas (TCGA) database, we analyzed PHF6 expression in pan-cancer. We first evaluated the relevance between PHF6 and prognosis; then, the relevance between PHF6 and immune cell infiltration in pan-cancer were analyzed. Subsequently, we explored the correlation between PHF6 and cancer heterogeneity, such as tumor mutation burden (TMB) and microsatellite instability (MSI), as well as cancer stemness. Finally, the role of PHF6 was validated in liver cancer and pancreatic cancer cell lines by cell proliferation assays. Results: PHF6 expression was higher in the vast majority of cancers than their normal counterparts. PHF6 was substantially correlated with prognosis and immune cell infiltration in various cancers. Moreover, PHF6 expression showed a strong correlation with cancer heterogeneity and stemness in certain cancer types. Additionally, the depletion of PHF6 inhibited cell proliferation in both liver and pancreatic cancer cells. Conclusions: PHF6 expression was closely associated with the occurrence and development of many types of cancer, and it might promote cancer progression by inhibiting the function of the immune microenvironment, while knockout of PHF6 significantly inhibited the tumor cells proliferation.