Allow editing the staff to have unreasonably long phone number

[DesmondTo]

Step to reproduce:

1. Enter the command `edit -n Candice p/888888888888888888888888888888888888888888888888888888888888888888888'

Expected: Not allow to add this unreasonably long phone number/Warning given.

Actual: Allow adding unreasonably long phone number. No warning given.

[nus-pe-bot]

Team's Response

There is no restriction on the length of phone numbers.

Items for the Tester to Verify

:question: Issue response

Team chose [response.Rejected]

• [ ] I disagree

Reason for disagreement: [replace this with your explanation]

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