This paper constitutes Stage X of an independent Phase–Scalar research program developed between 2025–2026. It introduces the Phase–Scalar Spiral as a universal diagnostic for identifying why complex systems fracture as they scale. Across mathematics, physics, distributed computing, artificial intelligence, biological systems, and organizational systems, recurring failure modes appear when systems scale: paradoxes in infinite constructions, divergences and "ghosts" in certain quantization programs, coordination breakdowns in distributed systems, hallucinations in large language models, dysregulated growth in biological systems, and metric-induced breakdowns in human institutions. These phenomena are typically treated as domain-specific anomalies. This paper proposes a unifying diagnostic explanation: many scale-failures are representational mismatches generated when global measurement and abstraction (Scalar) outrun local relational coordination (Phase). Building on Phase–Scalar Reconstruction (PSR) and the Spiral Coordinate System (SCS), we formalize a general principle: coherence is preserved when Phase precedes Scalar at each recursive level of growth. We present the Phase–Scalar Spiral as an applied synthesis: a cross-domain lens that explains why locality-preserving methods (e.g., renormalization, neighborhood-based computation, context-grounded inference) stabilize systems, while scalar-first expansions often produce artifacts (divergence, paradox, hallucination, institutional dysfunction). The contribution is methodological and diagnostic: it proposes no new physical laws and does not modify established domain formalisms. Instead, it offers a disciplined way to classify when a problem is ill-posed due to category collapse, and how to restore coherence by re-establishing local coordination before re-scaling.