The quantum measurement problem—the absence of any dynamical mechanism connecting continuous wavefunction evolution to discrete empirical outcomes—has persisted since the foundations of quantum theory. Decoherence explains interference suppression but cannot explain outcome selection: the diagonal density matrix remains an improper mixture until one outcome is actualized. We propose that collapse is a physical phase transition in the coupled system—apparatus field. The order parameter ψ, constructed as a conditional collective coordinate of apparatus degrees of freedom, evolves under time-dependent Ginzburg—Landau (TDGL) dynamics with a symmetry-breaking potential. When the coherence pressure γ ≡ g √N|⟨Sˆ⟩|/ℏωS exceeds a critical threshold γc = λ/ℏωS, the symmetric phase (superposition) becomes unstable and the field crystallizes into one of the discrete stable minima (eigenstates). We derive the critical coupling from microscopic system—apparatus Hamiltonians,obtaining the scaling gc ∼ N−1/2, which explains why macroscopic apparatus collapse wavefunctions while microscopic interactions preserve coherence. The TDGL dynamics are derived from the microscopic Hamiltonian via the Schwinger—Keldysh path integral, with each step a controlled approximation requiring no modification to the Schr¨odinger equation. The Born rule Pn = |cn|2 is preserved through a dynamical selection mechanism: an equal-basin-volume theorem—proved from the permutation symmetry of the apparatus interaction—ensures that attractor basin geometry under probability-conserving Fokker—Planck flow converts quantum amplitudes into outcome probabilities. We characterize the quantum-classical interface via two complementary classicality criteria and identify a four-stage measurement chain (unitary evolution → decoherence → coarse-graining → phase transition) that resolves the Heisenberg cut dynamically. The theory yields four falsifiable predictions absent from standard quantum mechanics: critical slowing near γc, hysteresis in the collapse—recoherence cycle, metastable supercooled superpositions,and transient Jacobian spikes at the moment of collapse. Quantitative estimates are provided for three experimental platforms—superconducting transmon readout, cavity QED with Rydberg atoms, and optomechanical systems—with explicit falsification criteria. This framework provides a concrete existence proof that collapse dynamics can be constructed from standard quantum mechanics plus statistical mechanics.