Deprecating phase in rollout status

# Summary

What change needs making?

- Deprecating phase in the rollout status following the guidance of [k8s API convention](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/api-conventions.md#spec-and-status)

- infer the rollout status from its conditions

# Use Cases

When would you use this?

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**Message from the maintainers**:

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Start by reading the Kubernetes API conventions guidance linked in the issue, then inspect the rollout status model and its conditions in the repository. Identify all uses of the phase field and the existing status calculation paths. Done means the phase is deprecated and rollout status is inferred from conditions without leaving affected users or callers inconsistent.

Written by the indexing model from the issue text.