Fix wording.

Signed-off-by: Revital Sur <eres@il.ibm.com>

Author: revit13

docs/metrics.coord.md

@@ -46,7 +46,8 @@ three to follow a request end to end.
 
 ## Labels
 
-Two labels use the words `encode`, `prefill`, and `decode`. They are not interchangeable.
+The `step` and `phase` labels both take the values `encode`, `prefill`, and `decode`, and are not
+interchangeable: a step is a pipeline stage, a phase is a single backend call.
 
 The **`step` label** names a stage of the coordinator's internal pipeline, observed once per request
 per stage. A step covers local work, orchestration, and any backend calls that stage makes. The
@@ -72,6 +73,10 @@ The first three values match the epp-profile header the coordinator sends. `cond
 not: the probe carries the decode profile header, like the decode step, and is distinguished by the
 `Prefer: if-available` header it adds. See the [Upstream phase family](#upstream-phase-family).
 
+The **`decision_type` label** names which phases a request ended up running, one value per request
+rather than per stage or per call: `decode-only`, `prefill-decode`, or `encode-prefill-decode`. See
+[`disagg_decision_total`](#disagg_decision_total).
+
 ## Error classes
 
 `error_code` on `request_error_total` and `pipeline_step_errors_total` uses one set of four values: