Housing staff must change only the contact-phone field on a waitlist entry without replacing the entire record. Which HTTP method fits that partial update?

Housing staff changing only the contact-phone field on a waitlist entry need HTTP PATCH to apply a partial update. PATCH sends a sparse modification—just the phone field (or a patch document describing that change)—so other waitlist attributes remain intact. That is the correct method when the business intent is a narrow field edit rather than rewriting the entire waitlist resource.

PUT that requires resending the complete waitlist resource every time fails this scenario's "only the contact-phone field" constraint: full replacement risks wiping fields the client did not intend to change if the complete document is stale or incomplete. GET cannot modify server-side fields; it is read-only and will not update the phone number. DELETE removes the waitlist entry entirely, which is the opposite of updating a single field and would destroy the resident's place in line.

Exam caveat: if an API does not implement PATCH, clients sometimes emulate partial updates carefully with PUT by read-modify-write, but that is riskier and not what this question asks. Prefer PATCH when the exam contrasts partial versus full replace.

Operational check: PATCH only the phone field on a test waitlist record, GET the resource and confirm other fields unchanged, attempt a mistaken DELETE in non-prod only to validate safeguards, and ensure production automation never uses PUT with partial bodies unless the API contract explicitly defines that behavior.