Recent observations from DESI and other surveys reveal two seemingly independent cosmologicaltensions. Dark energy exhibits late-time deviation from a cosmological constant (w0 = −0.70±0.09),while structure growth shows low-redshift suppression relative to CMB-inferred expectations.We show that both effects can be consistently interpreted within a single phenomenological framework based on loss of phase accessibility in an expanding universe. From an effective late-timedescription, we derive specific, testable functional forms for w(z) and σ8(z), governed by a singleeffective coupling parameter γ0 ≃ 0.16—0.20, achieving quantitative agreement with current data.The framework predicts a scaling correlation between dark energy evolution and structure growthsuppression that is not reproduced by ΛCDM or standard extensions. These results suggest thatcosmic acceleration and late-time structure formation may be understood as coupled manifestationsof effective phase dynamics, rather than independent phenomena requiring separate explanations.