Phishing websites remain a persistent cybersecurity threat by mimicking legitimate sites to steal sensitive user information. Existing machine learning–based detection methods often rely on supervised learning with labeled data, which not only incurs substantial annotation costs but also limits adaptability to novel attack patterns. To address these challenges, we propose PhishSSL, a self-supervised contrastive learning framework that eliminates the need for labeled phishing data during training. PhishSSL combines hybrid tabular augmentation with adaptive feature attention to produce semantically consistent views and emphasize discriminative attributes. We evaluate PhishSSL on three phishing datasets with distinct feature compositions. Across all datasets, PhishSSL consistently outperforms unsupervised and self-supervised baselines, while ablation studies confirm the contribution of each component. Moreover, PhishSSL maintains robust performance despite the diversity of feature sets, highlighting its strong generalization and transferability. These results demonstrate that PhishSSL offers a promising solution for phishing website detection, particularly effective against evolving threats in dynamic Web environments.